Replaced Pygments with Rouge. See issue https://github.com/gollum/gollum-lib/issues/41

Replaced Pygments with Rouge. See issue https://github.com/gollum/gollum-lib/issues/41 . Modified tests to conform to Rouge's output, because Rouge does not add redundant \<div\> tags to markup. All tests are passing. Highlighting seems to be working in order, but please test functionality carefully. Thanks to @dometto for his contributions.