Bugs

* After exiting (:q) a buffer that has diff enabled, subsequent diffs appear to fail.
* Should restore options like 'wrap' to their original state when turning diff off
* winsaveview() and winrestview() require Vim 7.x. Autodetect and degrade gracefully.

Features

* Option to show side-by-side diff (ie. don't hide original buffer)
* Make it easier to customize colors and commands
* Add a refresh or enable an auto-update feature so diff highlighting changes as changes are made.