Add projT1_path_sigma_uncurried

This way, the theorems match the structure of `path_sigma{,_uncurried}`.
Add some more symlinks to fix anomalies

This closes #201.
Merge pull request #214 from JasonGross/fix-symlinks

Add some more symlinks to fix anomalies
Merge pull request #209 from JasonGross/proj-path-sigma-uncurried

Add projT1_path_sigma_uncurried
Make [sigT] an alias for [sig].

Now we only need to use [sig], [exist], and can choose either [proj1],
[proj1_sig], or [projT1] for its first projection (and similarly for its
second projection).  Because [proj1] used to be for [and], which is now
a notation for [prod], I've added a coercion [prod >-> sig] which allows
us to use [proj1] in place of [fst] and [proj2] in place of [snd].
Additionally, I've made the parameters for [proj1] and [proj2] implicit
and maximally inserted, so that we can do things like [ap proj1] and
have it mean what we want it to (that is, [ap proj1] is [ap (@proj1 _
_)]).  It would be nice to unify [Coq.Init.Specif] and
[Coq.Init.Datatypes], and make [fst] and [snd] just puns of [proj1] and
[proj2], maybe, but I think Coq will complain if I move identifiers
between files.
Don't use proj1; introduce pr1 in Overture.v
Merge pull request #208 from JasonGross/unify-sig-sigT

Make [sigT] an alias for [sig].
Define some variants of transport_path_prod

It's a reduction rule for transport across path_prod.
Merge pull request #218 from JasonGross/path_prod

Looks ok, but please don't start every comment with the word "now" :-)
Define some variants of transport_path_prod
Update path to github so that it works

This unbreaks the copying of files from github in the absence of
autoreconf.
Don't add files to git index; make travis check

Now, travis will (hopefully) actually try to build this without
autoreconf.  Also, ./autogen.sh no longer adds files to the index.
Only fallback on git if autoreconf not found
Bundle coq as a git submodule

This will hopefully pave the way to make it easier to build coq for new
users.
Update travis to build the git submodule coq
Update INSTALL.txt

It now explains how to use the travis scripts to install Coq
automatically, and how to use the bundled version to not have to manage
branches.
Make separate etc/install_coq.sh script for users
Improve installation instructions
Remove useless -j
Incorporate @JasonGross's suggestions