Gitx dev diff word highlight

Integrated an inline word diff algorithm to highlight changed words in diffs. similar to github's hybrid mode. 
Addressing  #168

The javascript implementation is based on John Resig's javascript diff algorithm described here: http://ejohn.org/projects/javascript-diff-algorithm/

![diff-testfile](https://f.cloud.github.com/assets/26716/967411/7a342be2-0577-11e3-898e-844ea0f24eb2.png)

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Known Issues
- [x] fix "stage line" behaviour when clicking on highlighted words
- [x] fix invalid diff displayed e.g. just append something at the end of a line
- [x] fix highlight of indention changes e.g. tabs to spaces: need to preserve tabs when passing diff data to javascript, currently tabs are already replaced by spaces
- [x] ~~fix diff view keeps showing "This is a large commit..." for some commits... need to figure out what's happening...~~ invalid

Bonus Todos
- ~~allow diff colors to be customized via `git config`~~ superseded by #249 
- [x] display file renames inline, e.g. very/long/path/to/{ old -> new }-filename.html