New documentation with DFM's sphinx theme

Adapted @dfm's sweet sphinx theme from encee to use here. Using Adobe Source Sans and Code via Google Fonts. Using a retina-ready github fork ribbon.

The documentaion content is a bit more elaborate. Made a separate page for installation instructions. Two API reference pages for the StellarPopulation class and fsps.filters module, respectively. These pages start with an example, then do sphinx-autodoc API. Also included a table of FSPS filters generated with the fsps_filter_table.py script.

![index](https://cloud.githubusercontent.com/assets/349384/3421631/17e20552-fef7-11e3-8eea-115a418bda2a.png)

![modelling](https://cloud.githubusercontent.com/assets/349384/3421632/2102c6f8-fef7-11e3-802c-a9b3b800073c.png)

![working_with_filters](https://cloud.githubusercontent.com/assets/349384/3421633/26752e0a-fef7-11e3-9fef-66fff5115de9.png)

![filters](https://cloud.githubusercontent.com/assets/349384/3421634/2bd035a2-fef7-11e3-90a4-64d608d84efe.png)