Add image of current travis build status to readme

This way we'll get to see the current build status from the
homepage (https://github.com/HoTT/HoTT).
Merge pull request #283 from JasonGross/readme-build-status

Add image of current travis build status to readme
links HoTTBook, Ch. 2.10-15 -> library
Define the functor (C -> D)^op -> (C^op -> D^op)

Unfortunately, it's a bit slow.  I'm not sure what to do to speed it
up...

Also, fine tune some other definitions so that we can get more proofs by
convertibility.

After    | File Name                                                | Before
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8m16.57s | Total                                                    | 8m10.57s
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1m45.33s | categories/Comma/ProjectionFunctors                      | 1m54.58s
0m33.53s | categories/Adjoint/Composition/AssociativityLaw          | 0m33.70s
0m23.99s | categories/Grothendieck/PseudofunctorToCat               | 0m24.88s
0m17.52s | categories/ExponentialLaws/Law4/Functors                 | 0m17.41s
0m16.65s | categories/Adjoint/UnitCounitCoercions                   | 0m17.46s
0m16.31s | categories/Comma/InducedFunctors                         | 0m15.39s
0m13.60s | categories/FunctorCategory/Dual                          |   N/A
0m13.00s | categories/Pseudofunctor/Core                            | 0m12.76s
0m12.90s | hit/Flattening                                           | 0m13.32s
0m11.90s | categories/Adjoint/Composition/Core                      | 0m12.35s
0m11.63s | categories/Adjoint/Dual                                  | 0m11.43s
0m11.42s | categories/Adjoint/Composition/IdentityLaws              | 0m10.86s
0m10.58s | categories/Pseudofunctor/FromFunctor                     | 0m10.75s
0m09.71s | categories/Functor/Pointwise/Properties                  | 0m09.48s
0m08.46s | categories/GroupoidCategory/Morphisms                    | 0m08.02s
0m08.29s | categories/Functor/Prod/Universal                        | 0m08.15s
0m08.20s | categories/ExponentialLaws/Law1/Law                      | 0m07.98s
0m07.53s | hit/Connectedness                                        | 0m07.52s
0m07.03s | categories/UniversalProperties                           | 0m07.15s
0m06.82s | categories/Adjoint/Paths                                 | 0m06.41s
0m06.54s | categories/Comma/Dual                                    | 0m06.12s
0m06.46s | categories/Adjoint/UnitCounit                            | 0m05.84s
0m06.09s | categories/Functor/Paths                                 | 0m06.09s
0m05.99s | categories/Category/Morphisms                            | 0m06.03s
0m05.83s | categories/DualFunctor                                   | 0m05.37s
0m05.60s | categories/Functor/Sum                                   | 0m05.81s
0m05.07s | EquivalenceVarieties                                     | 0m05.20s
0m04.92s | categories/ExponentialLaws/Law2/Functors                 | 0m04.96s
0m04.19s | categories/Category/Sigma/OnMorphisms                    | 0m04.16s
0m03.91s | types/ObjectClassifier                                   | 0m03.56s
0m03.61s | categories/ProductLaws                                   | 0m03.64s
0m03.16s | categories/FunctorCategory/Morphisms                     | 0m01.62s
0m03.10s | types/Sigma                                              | 0m03.20s
0m03.07s | categories/Adjoint/UniversalMorphisms                    | 0m02.74s
0m03.04s | categories/Functor/Prod/Functorial                       | 0m02.88s
0m02.82s | categories/FunctorCategory/Functorial                    | 0m02.68s
0m02.58s | categories/Grothendieck/ToSet                            | 0m02.54s
0m02.46s | Equivalences                                             | 0m02.58s
0m02.25s | categories/Category/Sum                                  | 0m02.27s
0m02.24s | categories/Functor/Attributes                            | 0m02.33s
0m02.11s | categories/Category/Sigma/Core                           | 0m02.09s
0m02.04s | categories/Comma/Core                                    | 0m02.03s
0m01.93s | PathGroupoids                                            | 0m02.02s
0m01.91s | categories/NaturalTransformation/Dual                    | 0m01.92s
0m01.90s | categories/NaturalTransformation/Isomorphisms            | 0m01.84s
0m01.72s | categories/NaturalTransformation/Paths                   | 0m01.74s
0m01.68s | categories/HomFunctor                                    | 0m01.83s
0m01.40s | categories/Category/Sigma/OnObjects                      | 0m01.41s
0m01.33s | categories/Category/Prod                                 | 0m01.39s
0m01.30s | categories/NaturalTransformation/Pointwise               | 0m01.35s
0m01.26s | types/Prod                                               | 0m01.28s
0m01.24s | categories/NaturalTransformation/Composition/Laws        | 0m01.74s
0m01.10s | categories/Limits/Core                                   | 0m01.12s
0m01.10s | categories/ExponentialLaws/Law1/Functors                 | 0m00.96s
0m01.08s | categories/ExponentialLaws/Law  N/A                      | 0m01.03s
0m01.06s | categories/Functor/Pointwise                             | 0m01.07s
0m01.06s | categories/CategoryOfSections/Core                       | 0m01.10s
0m01.00s | categories/NaturalTransformation/Prod                    | 0m00.96s
0m00.91s | hit/Spheres                                              | 0m01.01s
0m00.88s | categories/Functor/Prod                                  | 0m00.87s
0m00.87s | types/Paths                                              | 0m00.88s
0m00.85s | hit/epi                                                  | 0m00.85s
0m00.85s | Trunc                                                    | 0m00.83s
0m00.81s | categories/Functor/Composition/Functorial                | 0m00.85s
0m00.69s | types/Universe                                           | 0m00.63s
0m00.67s | categories/InitialTerminalCategory                       | 0m00.68s
0m00.65s | categories/NaturalTransformation/Composition/Core        | 0m01.35s
0m00.58s | types/Sum                                                | 0m00.62s
0m00.58s | Functorish                                               | 0m00.57s
0m00.58s | hit/quotient                                             | 0m00.54s
0m00.56s | categories/NaturalTransformation/Sum                     | 0m00.52s
0m00.54s | categories/Functor/Composition/Laws                      | 0m00.47s
0m00.52s | categories/Limits/Functors                               | 0m00.46s
0m00.52s | hit/Suspension                                           | 0m00.51s
0m00.52s | categories/categories                                    | 0m00.48s
0m00.52s | categories/Comma/Projection                              | 0m00.59s
0m00.50s | types/Record                                             | 0m00.47s
0m00.50s | hit/Circle                                               | 0m00.53s
0m00.47s | types/Forall                                             | 0m00.45s
0m00.45s | categories/ExponentialLaws/Law3/Functors                 | 0m00.45s
0m00.45s | Tactics                                                  | 0m00.46s
0m00.45s | categories/KanExtensions/Functors                        | 0m00.44s
0m00.43s | categories/Cat/Core                                      | 0m00.44s
0m00.41s | HProp                                                    | 0m00.42s
0m00.40s | HSet                                                     | 0m00.41s
0m00.39s | categories/Functor/Functor                               | 0m00.32s
0m00.38s | categories/NaturalTransformation/Identity                | 0m00.32s
0m00.35s | categories/NaturalTransformation/Composition/Functorial  | 0m01.26s
0m00.35s | Fibrations                                               | 0m00.34s
0m00.34s | TruncType                                                | 0m00.35s
0m00.32s | categories/IndiscreteCategory                            | 0m00.29s
0m00.31s | categories/Functor/Dual                                  | 0m00.30s
0m00.29s | hit/minus1Trunc                                          | 0m00.29s
0m00.29s | categories/KanExtensions/Core                            | 0m00.66s
0m00.28s | categories/Cat/Morphisms                                 | 0m00.28s
0m00.26s | Misc                                                     | 0m00.28s
0m00.26s | types/Arrow                                              | 0m00.26s
0m00.25s | categories/ExponentialLaws/ExponentialLaws               | 0m00.28s
0m00.24s | categories/Utf8                                          | 0m00.25s
0m00.24s | categories/Category/Objects                              | 0m00.23s
0m00.24s | categories/Grothendieck/Grothendieck                     | 0m00.27s
0m00.23s | categories/Grothendieck/ToCat                            | 0m00.20s
0m00.22s | categories/DependentProduct                              | 0m00.21s
0m00.22s | categories/Adjoint/Adjoint                               | 0m00.22s
0m00.21s | categories/SetCategory/Functors/Functors                 | 0m00.18s
0m00.21s | categories/Functor/Composition/Core                      | 0m00.23s
0m00.20s | Conjugation                                              | 0m00.22s
0m00.20s | categories/Comma/Utf8                                    | 0m00.14s
0m00.20s | categories/Adjoint/Identity                              | 0m00.15s
0m00.20s | categories/GroupoidCategory/Core                         | 0m00.20s
0m00.20s | categories/Notations                                     | 0m00.22s
0m00.19s | categories/Limits/Limits                                 | 0m00.16s
0m00.19s | categories/NaturalTransformation/NaturalTransformation   | 0m00.23s
0m00.18s | categories/Cat/Cat                                       | 0m00.16s
0m00.18s | categories/FunctorCategory/Utf8                          | 0m00.15s
0m00.18s | hit/iso                                                  | 0m00.22s
0m00.18s | categories/Category/Dual                                 | 0m00.16s
0m00.18s | categories/Comma/Comma                                   | 0m00.16s
0m00.18s | categories/NatCategory                                   | 0m00.20s
0m00.18s | categories/ExponentialLaws/Law2/Law2                     | 0m00.13s
0m00.17s | categories/KanExtensions/KanExtensions                   | 0m00.15s
0m00.17s | categories/Functor/Prod/Prod                             | 0m00.20s
0m00.17s | contrib/HoTTBook                                         | 0m00.14s
0m00.17s | categories/FunctorCategory/FunctorCategory               | 0m00.16s
0m00.17s | categories/Comma/Notations                               | 0m00.13s
0m00.17s | categories/Category/Category                             | 0m00.16s
0m00.17s | FunextVarieties                                          | 0m00.17s
0m00.17s | categories/FunctorCategory/Core                          | 0m00.18s
0m00.16s | categories/SetCategory/Core                              | 0m00.13s
0m00.16s | HoTT                                                     | 0m00.15s
0m00.16s | categories/Adjoint/Notations                             | 0m00.16s
0m00.16s | categories/Adjoint/Composition/Composition               | 0m00.18s
0m00.16s | categories/Functor/Utf8                                  | 0m00.15s
0m00.16s | categories/Profunctor/Representable                      | 0m00.12s
0m00.16s | categories/Pseudofunctor/Pseudofunctor                   | 0m00.16s
0m00.16s | categories/NaturalTransformation/Notations               | 0m00.19s
0m00.16s | categories/Category/Core                                 | 0m00.14s
0m00.15s | categories/Adjoint/Utf8                                  | 0m00.13s
0m00.15s | categories/Functor/Notations                             | 0m00.14s
0m00.15s | categories/Category/Univalent                            | 0m00.13s
0m00.15s | hit/Truncations                                          | 0m00.12s
0m00.15s | categories/CategoryOfSections/CategoryOfSections         | 0m00.13s
0m00.14s | hit/unique_choice                                        | 0m00.17s
0m00.14s | categories/Category/Subcategory/Wide                     | 0m00.10s
0m00.14s | categories/NaturalTransformation/Core                    | 0m00.16s
0m00.14s | categories/Profunctor/Identity                           | 0m00.12s
0m00.14s | categories/NaturalTransformation/Utf8                    | 0m00.12s
0m00.14s | categories/FunctorCategory/Notations                     | 0m00.09s
0m00.14s | categories/Adjoint/Composition/LawsTactic                | 0m00.15s
0m00.13s | categories/Category/Utf8                                 | 0m00.12s
0m00.13s | categories/Profunctor/Profunctor                         | 0m00.11s
0m00.13s | types/Bool                                               | 0m00.14s
0m00.13s | categories/ExponentialLaws/Law1/Law1                     | 0m00.15s
0m00.13s | categories/Category/Sigma/Sigma                          | 0m00.12s
0m00.13s | categories/Functor/Composition/Composition               | 0m00.18s
0m00.13s | categories/Category/Subcategory/Full                     | 0m00.07s
0m00.12s | categories/GroupoidCategory/GroupoidCategory             | 0m00.08s
0m00.12s | categories/Profunctor/Notations                          | 0m00.12s
0m00.12s | coq/Init/Peano                                           | 0m00.10s
0m00.12s | categories/Category/Subcategory/Subcategory              | 0m00.12s
0m00.12s | categories/Category/Notations                            | 0m00.13s
0m00.12s | types/Unit                                               | 0m00.14s
0m00.12s | categories/Functor/Pointwise/Pointwise                   | 0m00.12s
0m00.12s | Overture                                                 | 0m00.13s
0m00.11s | categories/ExponentialLaws/Law3/Law3                     | 0m00.15s
0m00.11s | categories/Adjoint/Core                                  | 0m00.14s
0m00.11s | categories/Profunctor/Core                               | 0m00.12s
0m00.11s | hit/Interval                                             | 0m00.13s
0m00.11s | categories/Functor/Core                                  | 0m00.10s
0m00.11s | categories/SetCategory/SetCategory                       | 0m00.10s
0m00.11s | categories/NaturalTransformation/Composition/Composition | 0m00.10s
0m00.10s | categories/ExponentialLaws/Law4/Law4                     | 0m00.08s
0m00.10s | categories/Profunctor/Utf8                               | 0m00.12s
0m00.09s | categories/DiscreteCategory                              | 0m00.12s
0m00.09s | Pointed                                                  | 0m00.08s
0m00.08s | categories/Functor/Identity                              | 0m00.07s
0m00.08s | Contractible                                             | 0m00.09s
0m00.08s | UnivalenceAxiom                                          | 0m00.10s
0m00.07s | categories/Category/Strict                               | 0m00.07s
0m00.07s | coq/Init/Specif                                          | 0m00.08s
0m00.07s | FunextAxiom                                              | 0m00.07s
0m00.06s | coq/Init/Datatypes                                       | 0m00.04s
0m00.06s | coq/Program/Tactics                                      | 0m00.05s
0m00.04s | coq/Init/Logic                                           | 0m00.03s
0m00.04s | coq/Init/Tactics                                         | 0m00.04s
0m00.04s | coq/Init/Logic_Type                                      | 0m00.06s
0m00.04s | types/Empty                                              | 0m00.08s
0m00.03s | coq/Init/Prelude                                         | 0m00.04s
0m00.02s | coq/Init/Notations                                       | 0m00.03s
0m00.02s | coq/Bool/Bool                                            | 0m00.03s
Merge pull request #287 from JasonGross/functor-category-op

Define the functor (C -> D)^op -> (C^op -> D^op)
Merge pull request #286 from marcbezem/master

Done with references HoTTBook, Ch.2 -> library (second try)
Fix @marcbezem's "double entry" and put in more instructions on how to use HoTTBook.v
Merge pull request #288 from andrejbauer/master

Fix @marcbezem's "double entry" 

I am pulling this in because #286 introduced a problem that this pull request fixes.