Will/src snippets

Uses the pygments library to include snippets from source files showing which lines are uncovered.

It looks like this:
![image](https://f.cloud.github.com/assets/2948394/989509/eb748fa8-0915-11e3-862b-0fd754e7441d.png)

Currently, this is implemented only in the coverage report, not the quality reports.

Suggested reviewers: @sarina @jzoldak