more [draw] improvements for data structures:

*added outlet to [draw] to notify for events
*added svg-style event mousedown (more to come)
*added a "drag" event for convenience (similar to curve_motion)
*fixed default strokelinejoin per svg spec
*event "bubbling" so that the closest shape to front gets the notification
*added "bbox" method to turn off bbox calculation (similar to curve's -n flag)
*added a "pointerevents" method per svg-spec
*fixed skewx and skewy transforms to use degrees instead of radians