Added default image type "retro"

Somehow you missed a beautiful default image type _"retro"_.
![00000000000000000000000000000000](https://f.cloud.github.com/assets/2548610/1810536/b5415d92-6e2a-11e3-86b7-e3c592d4473b.png)
 
_Please merge this and publish to maven central :)_