get packaging working, seemingly

this commit:

 * adds a MANIFEST.in to pick up .hy and nltk_data
 * adds include_package_data = True to pick up the MANIFEST.in
 * fixes some imports
 * add a hack for dynamically finding nltk data

I can now install this into a venv with pip and include it from other projects.
Haven't tested beyond that, and the nltk data hack probably needs to be thought
through some more.