Renamer pass

Resolves #534, resolves #511.

Doesn't resolve #449. I tried moving the renaming pass up into desugaring before binding groups are created, but that has its own problems, as we need binding groups to be able to rename properly. Not to mention it could make compiler errors even harder to understand later on.

Please rip it to shreds, as although the test pass, `test-everything` compiles and `purescript-in-purescript` still runs I'm still nervous about it given how error prone this kind of thing can be.
I'm trying to understand the call to `lookup` to generate a new name. It sort of makes sense putting `newName` in the dictionary if we check the keys, but I'm trying to figure out if we should be checking the values instead.