FIX: Pinch state was not accurately calculated sometimes

FIX: Cursor string URLs were not working as intended.

CHANGE: The onscreen.lua module will now handle switch to multitouch mode on iOS. Thanks @aglitchman !

NEW: The gesture module will now report repeated on touch events. Thanks @Jerakin!

NEW: Added cursor.reset(url) to reset the state of a cursor. Useful when a window focus lost or minimize event happens and you want to clear the state of the cursor.
FIX: There is no longer a requirement that cursor.init() has been called before cursor.listener()

NEW: Programatically start a cursor drag operation (info: https://github.com/britzl/defold-input/blob/master/in/cursor.md#drag-objects)

NEW: Added origin_x and origin_y to drag event to give position of mouse/touch down
NEW: Added drag_event_only option to cursor to only send the drag event but not start dragging the object under the cursor

Thanks to @Trevortni for the contributions!

FIX: Clear drag state on release if drag was cancelled. Thanks @Trevortni

FIX: Don't ignore a potential drag (press move) just because the cursor moved outside of the object but hasn't yet reached the drag threshold.

FIX: Cancelled drag events prevented further drag events