Add hover effect with transition to `#forkme_banner`

Makes the "Fork me on GitHub" banner look a bit fancier when you hover over it. To see the result in action, see:

* http://static.iqandreas.com/

The colors used were basically picked arbitrarily from "what looked good" in an online color-picker, and are open to suggestions _(Damn it, man, I'm a developer, not a designer!)_.