Modified scrolling to use CADisplayLink instead of NSTimer.
Much less CPU intensive and avoids having to choose a timer interval, which due
to a bug was being set a 0.001 milliseconds (10,000 times per second!)
Multplied scrollRate by a factor of 10 for faster scrolling.
Added draggingViewOpacity property to making the opacity of the
dragging view configurable. Defaults to 1.0 (completely opaque).
Merge pull request #15 from mluisbrown/master

Modified scrolling to use CADisplayLink instead of NSTimer.