Meta: Vendoring

[sgraf812]

Currently, although we have module merging, vendoring is not implemented. It's not terribly complicated to do so, just time consuming and not really research-y.

1. Do something like cabal get containers-0.6.0.1 to get a local checkout. That's the "vendoring" part.
2. Add source dir to current project's cabal file's library
3. Copy over other sections, like other-modules etc.
4. The last two steps are so that everything is treated as a single library that can be loaded into the GHC API, the module graph of which we can then merge with HsAllInOne.