Package.

While I haven't uploaded this to PyPI (since it's not mine), I have built and
installed it locally, so I'm reasonably confident it all works.
Add Sphinx documentation-generation files.

I ignored the actual generated files under the assumption you'd use
ReadTheDocs, which generates them itself.
Add invoke tasks.

It's so much nicer than remembering all these different commands, neh?
Alter docstrings to use Sphinx-parseable syntax.