Touch event support

[jxson]

I recently worked on a project that needed touch events and found the lack of them in mercury a bit tough. Specifically the touchstart event is a must since it is the entry point for any custom event handling that might need to happen (similar to the geometry example where the custom drag-handler was added via ev-mousedown).

Other events to consider would be:

• touchend
• touchcancel
• touchleave'

[Raynos]

you can delegator.listenTo('touchstart') to add it to the whitelist.

The thing missing here is more obvouis documentation

[jxson]

fixed in PR #6