Convert theme to a python package

This allow a user to install this theme as a python
package.

In certain situations (specifically when I was building docs with this theme installed in a virtualenv) I would get these errors:

```
<partial node>:: (ERROR/3) Cannot embed stylesheet '../../../../.virtualenvs/14ac3e438672380f/lib/python2.7/site-packages/docutils/writers/html4css1/html4css1.css': No such file or directory.
```

Seems that other people are running into this and should (hopefully) by fixed in a later version of docutils.