Convert the documentation from Lore to Sphinx

It's not great, I'm not sure how to exactly convert the more "prose" style of the old documentation to the more "automated" way of linking documents together by Sphinx.

Still, it's pretty good I guess, it should fix #20 and allow with some more help to fix #21  as well.
Ideally, the version number would not be duplicated here (9/10ths of the motivation for switching to github was to get rid of the duplicate version number in `setup.py`, I'd really like to not immediately re-introduce the duplication in another place).