Adding a 'Front Page' to the RHS Table of contents

re Issue: #72.  Added a "Front Page" to the Table of Contents, which points to the front page of the document (_i.e._ index.html).

I've wrapped it up into a separate <ul> (there doesn't seem to be a way of changing the toctree directly without causing other problems), and made the entry slightly darker than the rest, just to distinguish it slightly.