Case-sensitivity now supported in import rewrite

I just finished running the test suite with case-sensitivity implemented and everything passed that should pass! That should place me at semantic completeness!

I still need to go through the code once and the docstrings for a basic cleanup. After that I will need to probably write up official documentation, rename the module ('importer' is an interface so naming the module that is bad; maybe name it importlib?). Then I will probably need to tighten up the API so that not everything is exposed.

But boy does it feel good to finally have reached this point!