Callbacks added

I've cleaned up he code just a little here and there so it now passes all the tests in the jshint linter.
I also added the `onAnimationEnd` callbacks to the options and after webkit transitions end.

One question, though, could it be possible to add CSS3 transitions for other browsers? I've added this gist with animation support for several browsers using CSS3 (maybe you could use some of it): https://gist.github.com/1478085

And thank you so much for iScroll !!