Add and use 'extend' function to duplicae objects
Save duplicate of the pointer down event

On iOS it seems that the touch objects in event.touches are the same
objects from touchstart to touchend of a point of contact.

Because an action doesn't start until the pointer moves, there is a
difference between the coordinates saved in 'startCoords' and those that
are reported by the touchstart events's touch coordinates. This
difference caused an incorrect startOffset to be calculated for
snapping/restricting when elementOrigin/elementRect are used.

Closes https://github.com/taye/interact.js/issues/73
Add changeTouches arrays to test data
Don't set startCoords to actionstart event coords