added multi-touch gestures

More work needed here, but wanted to get some initial feedback.

I tested with two finger pinch, zoom, and pan and this works fine.

Issues here:
1. eventWithTouch was duplicated to make eventWithTouches, they should be merged.
2. dragPointsAlongPaths take an NSArray, not a CGPoint[] array. I can convert the old function to use NSArray(which I think is preferable), or, convert my code to use CGPoint[].
3. dragPointsAlongPaths assumes that all touches happen at the same time, and end at the same time. After looking at KIFEventProxy, I became less confident that this will work for arbitary lengths and touches.
4. Tests? What is the best way to write them? Some input would be nice.


This line was copied directly from the old implementation of eventWithTouch:

That said, I just noticed that said category interface was already defined, so I'm pushing a new PR with this line removed and swapped out.