Table of contents for the guide

This adds a JS TOC using this library https://github.com/ghiculescu/jekyll-table-of-contents

More precisely, it generates the table of contents for the current chapter just below the chapter title.

Preview:
![screen shot 2014-05-15 at 03 34 51](https://cloud.githubusercontent.com/assets/207748/2979215/f8bdb80c-dbc8-11e3-8826-f793a24ec220.png)