Pygments fix

This pull request does two things:
1. Tidies up the Pygments hook.
2. Adds a test for Pygments
3. Demonstrates that the use of relative imports (from ..hookutils instead of from hookutils) is required to pass the tests in #2.

Therefore, the last commit should **not** be merged, since it breaks the tests, per a request by Harmut to demonstrate a broken case. Everything up to the last commit should be merged.