add pointer events

[Garados007]

The pointer events are useful if you want to support mouse like behavior on a mobile screen because it combines the Apis for mouse, touch and normal pens.

This pull request adds three methods that enables the user to subscribe to the pointerdown, pointerup and pointermove events on the document node like onMouseUp, onMouseDown and onMouseMove would do with mouse events.

With this addition the community can create custom drag&drops, menus or drawing boards on mobile screens that behave like on a normal desktop computer.

[loicknuchel]

I just need that, would be awesome!