Proof of concept of using Sphinx to generate docs

[jeffkole]

This is the first step to publishing docs to readthedocs.io

The configuration allows us to write Markdown files that can reference source code objects (like link to the API documentation for Phase).

As it is, we need to explicitly list the source code objects we want to have documented, which is what you see in the api.md document. We probably should have a better structure for the API docs and, as you said last week, write docs for use cases more than strict API documentation.

[jeffkole]

To build the docs, run make html in the docs directory and open _build/html/index.html to see them in a browser.