Reorganize sphinx docs to more common format.

Format based off current best practices for sphinx docs:

- https://github.com/mitsuhiko/flask/tree/master/docs
- https://github.com/kennethreitz/requests/tree/master/docs
- https://github.com/saltstack/salt/tree/develop/doc


Output to ``_build``, ``index.rst`` in root. This should be compatible with readthedocs.org.