Added optional syntax highlighting to the diff viewer using the Pygments library. The result is very nice syntax highlighted code, and it still works with interline diffing and everything else. The only real downside is that it may take slightly longer to generate and display the code (though it shouldn't be a significant difference), and that the resulting HTML is bigger (a 60KB HTML page becomes around 100KB). For most setups, however, the download size shouldn't be an important factor.

This feature is disabled by default and must be turned on in settings_local.py.

Created and ran several unit tests. Made sure that all my test diffs displayed correctly.