Improved docs styling

![GeoAlchemy 2 Documentation GeoAlchemy2 0 1 documentation - Chromium_010](https://f.cloud.github.com/assets/141300/318398/49eb599a-9896-11e2-96ae-e4b12d8e0485.png)

![Elements GeoAlchemy2 0 1 documentation - Chromium_011](https://f.cloud.github.com/assets/141300/318399/4ee07214-9896-11e2-9918-7986f20014f6.png)