A CSS that looks more like GitHub.

Hi,

I updated the CSS file with the latest style used by GitHub.

This is a preview of the README.md of one of my projects:

![2013-10-17_17h11_02](https://f.cloud.github.com/assets/155998/1352941/620e74fc-373e-11e3-900e-78dbbe95a939.png)