Feature/sphinx docs

[quigleyj97]

This adds documentation using the Sphinx doc generator, including both reference docs for motorlib and a short doc on building.

This will give us a base to build off for further user docs, such as how-tos, a getting started guide, examples, tutorials, etc.

To build the docs, install Sphinx:

$ pip install sphinx
$ cd ./docs
$ sphinx--build -b html . _build

You can also use make html on *nix or make.bat html on Windows, once you have sphinx installed.

The generated docs will be in ./docs/_build/index.html and can be browsed using a normal web browser.

[reilleya]

Looks good to me. Think we should have something about the docs in the main readme?