(WIP) initial attempt at menpo3d docs

[jabooth]

This PR ports over menpofit's doc generation code to menpo3d. This doesn't include rst files - to generate them:

cd docs
pip install sphinx sphinx_rtd_theme sphinxmapxrefrole
python ./generate_rst.py

However this makes a set of rst files that aren't really optimal.

This PR is a starting point for getting this working.