Adding raw diff feature file
Adding a raw link and .diff format for a code review

* Added 'raw' link to code review
* Added custom diff mime-type
* Added new format for show action
Ensuring raw doesn't wrap on small screens
Changing '.expiry' to '.info'
Implemented cucumber steps for raw diff link
Merge pull request #1 from jakspalding/raw-diffs

Adding link to download raw diff file