Handling touchcancel

[gre]

Your library is missing a "touchcancel" binding which is really important to touchable device.

For instance, on an iPad, if you do a gesture during a drag it will stay the dragging element in an inconsistant state ("dragging" state while the touch has end).
With touch events, If you listen to "touchcancel" you can know something else has occured and you can stop the drag.

Awesome library otherwise.