Add xcpretty

Makes the build output nicer.

![bildschirmfoto 2014-05-25 um 12 34 19](https://cloud.githubusercontent.com/assets/759730/3076738/4b4864d2-e3f8-11e3-81ea-0660b2c28906.png)

Install with: `gem install xcpretty`

[More information](github.com/supermarin/xcpretty)