Add Sphinx-based documentation; convert existing docstrings

A solid start to issue #21 - this creates basic documentation with Sphinx, adds and exposes the API documentation, converts existing epydoc strings into Sphinx autodoc format, and converts the existing Readme over into reST format -- still displays nicely on GitHub with the .rst extension :)

If this looks good, then adding the repo to https://readthedocs.org/ will make it so that documentation gets automatically built on repository changes.