SingleTap event listener added

I've added a onSingleTapConfirmed() callback. 
It was useful because I wanted to hide/show actionbar on single tap like it is done in default Android Gallery app on Galaxy Nexus.
onSingleTapConfirmed() callback prevents the user of a lib from receiving DoulbeTap events when they only need to catch a single tap. 
Docs on this method are here: http://developer.android.com/reference/android/view/GestureDetector.SimpleOnGestureListener.html#onSingleTapConfirmed(android.view.MotionEvent)