Add mouse drag/fling support.

Hey @petehunt,

I’m exploring adding other input method support to this as is. I have a few concerns on my implementation I’d appreciate your feedback on.
`pointerevents` follow the mouse rules by default, but expose two additional methods to opt-in and out of the touch model at will.

* `setPointerCapture`
* `releasePointerCapture`

To see what this looks like in action check out: http://patrickhlauke.github.io/touch/tests/pointercapture.html 

Spec: http://www.w3.org/TR/pointerevents/#attributes-2
MSDN Docs: http://msdn.microsoft.com/en-us/library/ie/hh771882%28v=vs.85%29.aspx