Adding background colors + annotations

I wrote an implementation for the feature request, about setting background colors to fullcalendar http://code.google.com/p/fullcalendar/issues/detail?id=144. 

There might be some bugs, since I don't possess deep knowledge of fullcalendar code base (I've been playing with it maybe 2 days), but it should not break any existing functionality.

I would love to get any feedback about it or how to improve the code so that it can be merged to official branch.