Improved touch behavior

As explained in #10 it would be better to define a `touchcancel` event handler as well for cases where the touch event was ended abrupt.
I also added support for jQuery. jQuery actually emulates a normal event and provides the native event (touch event) as a property called `originalEvent`. To obtain the X and Y coördinates of the touch event, we need to retrieve it from `event.originalEvent.touches.item(0)` in stead of `event.touches.item(0)`. I added an additional `if` statement to verify if there is an `originalEvent` property defined or not. Without it, the touch events won't work when used in combination with jQuery.

I personally think jQuery should not wrap it, but I suppose they won't change that.