Support a touch API

[darkf]

Before any major public release, I'd like to include a touch API for the overwhelming number of people with tablets.

Suggested API:

heart.touch.getTouchPoints() - self explanatory

Callbacks:

heart.touchBegin(x, y)
heart.touchMove(x, y)
heart.touchEnd(x, y)

this is, of course, subject to change, since I know pretty much nothing about touch-oriented interfaces.