button-up?

Returns #t if the event is for a button release or #f otherwise.

• (send a-wx:mouse-event button-up? button) -> boolean
      button = -1 : small integer

  If button is -1, #t is returned if the event was a mouse button release event. If button is 1, 2, or 3, then #t is only returned if it is a release event for the left, middle, or right button, respectively.