Implementing Travis task to publish docs to static site

[captainrobbo]

Here's the plan to publish documentation smoothly. Since we need both npm/jsdoc and python/sphinx, we cannot use readthedocs. Instead we will follow what Mozilla's Fathom project does; they already have the same mix of Pythin and JS documented with Sphinx. See the heading "Example" in this page....

https://pypi.python.org/pypi/sphinx-js

So, we write a script which will build the docs in a separate subdirectory, and push them to the gh-pages branch of the athlib repo. This branch will be "docs and static stuff" only. It can be served from openath.github.io/athlib/

This can then be run for us by Travis, so a simple push of the code or docs is enough to update the hosted docs.