Add diff colors

Adds some color when using a diff with Sublime Text (for example, using [SublimeGit](https://sublimegit.net/))

Before:
![before](https://cloud.githubusercontent.com/assets/692077/2859431/1323de0c-d1a5-11e3-82b8-8e25293b0bed.jpg)

After:
![after](https://cloud.githubusercontent.com/assets/692077/2859432/18e8b4de-d1a5-11e3-90ee-b0ac657d48c3.jpg)