This achieves several goals:
* Less reliance on scripts so we have better portability to Windows
(though we still have a ways to go for proper Windows support).
Luajit, luarocks, moonscript, and busted are all installed via CMake
now.
* Trying to make use of pkg-config to get the correct libraries. The
latest libuv is still broken in this regard, but we'll at least be in
a position to use it.
* Allow the use of Ninja or make. The former runs faster in many
environments, and automatically makes use of parallel builds.
This also allows for system installed dependencies--though not through
the Makefile just yet--and adds support for FreeBSD.
This also make us build libuv and luajit as static libraries only, since
we're only concerned about having static libraries for our bundled
dependencies.
Add a brief README on the purpose of the third-party directory and some
suggestions for how to manage it. The neovim bigwigs may want to
re-draft the README.
