Update HoTT to have Unit in Set.

This works with the newest HoTT/coq, and fixes a universe inconsistency.
Make NatCategory a bit nicer

We now have, judgementally, that 0^op = 0 and 1^op = 1.

After    | File Name                             | Before
-----------------------------------------------------------
0m39.40s | Category/Equality                     | 0m40.75s
0m21.22s | NaturalTransformation/Equality        | 0m21.22s
0m17.30s | Functor/Equality                      | 0m17.11s
0m10.92s | Comma/Duals                           | 0m10.23s
0m10.52s | Comma/CommaCategory                   | 0m11.37s
0m09.14s | Groupoid                              | 0m09.30s
0m07.53s | Category/Morphisms                    | 0m07.61s
0m04.52s | Grothendieck/ToSet                    | 0m04.60s
0m03.83s | Groupoid/Functors                     | 0m04.08s
0m02.30s | SumPreCategory                        | 0m02.30s
0m02.18s | Functor/CompositionLaws               | 0m02.04s
0m02.16s | Category/Product                      | 0m01.97s
0m01.73s | NaturalTransformation/Duals           | 0m01.75s
0m01.33s | NaturalTransformation/Composition     | 0m01.30s
0m01.16s | NaturalTransformation/CompositionLaws | 0m01.17s
0m01.06s | InitialTerminalCategory               | 0m01.19s
0m00.97s | Comma/Projection                      | 0m01.08s
0m00.92s | NatCategory                           | 0m00.86s
0m00.63s | BoolCategory                          | 0m00.67s
0m00.52s | SetCategory                           | 0m00.53s
0m00.37s | Functor/Product                       | 0m00.38s
0m00.33s | IndiscreteCategory                    | 0m00.29s
0m00.28s | Common                                | 0m00.30s
0m00.26s | Functor/Duals                         | 0m00.20s
0m00.26s | Adjoint/UnitCounit                    | 0m00.24s
0m00.24s | FunctorPreCategory                    | 0m00.26s
0m00.24s | NaturalTransformation/Identity        | 0m00.31s
0m00.22s | Category/Objects                      | 0m00.24s
0m00.21s | Functor/Composition                   | 0m00.19s
0m00.20s | NaturalTransformation/Core            | 0m00.19s
0m00.18s | IsGroupoid                            | 0m00.20s
0m00.18s | NaturalTransformation/Product         | 0m00.16s
0m00.16s | Category/Duals                        | 0m00.18s
0m00.14s | Category/Core                         | 0m00.16s
0m00.14s | Peano                                 | 0m00.13s
0m00.13s | Category/Category                     | 0m00.10s
0m00.11s | ComputableCat                         | 0m00.12s
0m00.11s | Functor/Core                          | 0m00.14s
0m00.10s | NaturalTransformation                 | 0m00.11s
0m00.10s | DiscreteCategory                      | 0m00.09s
0m00.10s | Utf8                                  | 0m00.08s
0m00.09s | Functor/Identity                      | 0m00.12s
0m00.09s | Functor                               | 0m00.10s
0m00.08s | Category/StrictCategory               | 0m00.09s
0m00.08s | Grothendieck                          | 0m00.08s
0m00.05s | NotationsUtf8                         | 0m00.05s
0m00.04s | Notations                             | 0m00.04s
-----------------------------------------------------------
2m23.83s | Total                                 | 2m25.68s
Add the fact that nat categories are self-dual.
Update to a newer HoTT
Add discrete duals
Update nat category duals

After    | File Name                             | Before
-----------------------------------------------------------
0m39.36s | Category/Equality                     | 0m39.79s
0m21.15s | NaturalTransformation/Equality        | 0m21.71s
0m16.96s | Functor/Equality                      | 0m17.31s
0m10.92s | Comma/Duals                           | 0m10.10s
0m10.83s | Comma/CommaCategory                   | 0m10.92s
0m09.60s | Groupoid                              | 0m09.08s
0m07.37s | Category/Morphisms                    | 0m08.00s
0m04.61s | Grothendieck/ToSet                    | 0m04.63s
0m03.90s | Groupoid/Functors                     | 0m03.76s
0m02.32s | SumPreCategory                        | 0m02.38s
0m02.13s | Category/Product                      | 0m02.08s
0m02.12s | Functor/CompositionLaws               | 0m02.08s
0m01.74s | NaturalTransformation/Duals           | 0m01.72s
0m01.41s | NaturalTransformation/Composition     | 0m01.33s
0m01.23s | NaturalTransformation/CompositionLaws | 0m01.23s
0m01.10s | InitialTerminalCategory               | 0m01.18s
0m01.02s | Comma/Projection                      | 0m01.04s
0m00.93s | NatCategory                           | 0m01.02s
0m00.68s | BoolCategory                          | 0m00.64s
0m00.56s | SetCategory                           | 0m00.48s
0m00.44s | Discrete/Duals                        | 0m00.42s
0m00.39s | Functor/Product                       | 0m00.34s
0m00.34s | Common                                | 0m00.31s
0m00.33s | IndiscreteCategory                    | 0m00.28s
0m00.28s | NaturalTransformation/Identity        | 0m00.25s
0m00.27s | Adjoint/UnitCounit                    | 0m00.28s
0m00.26s | Functor/Composition                   | 0m00.24s
0m00.24s | Category/Objects                      | 0m00.20s
0m00.24s | NatCategory/Duals                     | 0m00.74s
0m00.23s | FunctorPreCategory                    | 0m00.24s
0m00.20s | Functor/Duals                         | 0m00.24s
0m00.19s | IsGroupoid                            | 0m00.22s
0m00.18s | NaturalTransformation/Core            | 0m00.18s
0m00.16s | Category/Core                         | 0m00.19s
0m00.16s | NaturalTransformation/Product         | 0m00.15s
0m00.15s | Functor/Core                          | 0m00.13s
0m00.15s | Category/Duals                        | 0m00.16s
0m00.11s | ComputableCat                         | 0m00.11s
0m00.11s | Category/Category                     | 0m00.11s
0m00.11s | DiscreteCategory                      | 0m00.08s
0m00.10s | Functor/Identity                      | 0m00.11s
0m00.10s | Category/StrictCategory               | 0m00.08s
0m00.10s | Peano                                 | 0m00.15s
0m00.09s | Utf8                                  | 0m00.08s
0m00.09s | Grothendieck                          | 0m00.08s
0m00.08s | NaturalTransformation                 | 0m00.10s
0m00.07s | Functor                               | 0m00.08s
0m00.06s | Notations                             | 0m00.04s
0m00.04s | NotationsUtf8                         | 0m00.03s
-----------------------------------------------------------
2m25.20s | Total                                 | 2m26.10s