Extend Mouse class to report horizontal scrolling

[narrowtux]

Hi, I wanted to get the horizontal scroll axis from the Mouse class.
At the moment, it combines both vertical and horizontal scrolling into the one axis that you can get with Mouse.getEventScroll or Mouse.getEventScrollD
It would be nice if that worked. Many trackpads (Apples one for example) and some mouses (Microsoft intelliExplorer 4.0 or the Mighty Mouse) support horizontal scrolling, the apple models do support both vertical and horizontal scrolling at the same time. So it would be nice if that would be refactored into
Mouse.getEventScrollDHorizontal()
Mouse.getEventScrollDVertical()
Mouse.getEventScrollHorizontal()
Mouse.getEventScrollVertical()
If you want to test stuff but don't have hardware for that, I'm happy to try it out on Mac OS X, Linux and Windows.