Return button release data

        Entry:
          AX = 0006h
          BX = button
              0 left
              1 right
              2 middle (Mouse Systems mouse)

        Return:
          AX = button states
               bit 0 left button pressed if 1
               bit 1 right button pressed if 1
               bit 2 middle button pressed if 1 (Mouse Systems mouse)
          BX = number of times specified button has been released since last call
          CX = column at time specified button was last released
          DX = row at time specified button was last released