Reorganize Package and Improve Documentation

Reorganize the RiveScript package: rivescript.py becomes
rivescript/__init__.py. Split the module into different files where it
makes sense: Interactive Mode was moved to rivescript/interactive.py,
and the Python object macro class was moved to rivescript/python.py.

Add brain/python.rs as an example of a Python object macro that encodes
text in Base64.

Improve documentation by switching to EpyDocs. All documentation is now
kept in the 'docs' folder.
Update setup.py and packaging rules