INT 33H 0014H: Exchange Mouse Event Handler

 Expects: AX    0014H
          CX    event mask (events which you want sent to your handler)
                  bit 0 = mouse movement           (CX | 01H)
                  bit 1 = left button pressed      (CX | 02H)
                  bit 2 = left button released     (CX | 04H)
                  bit 3 = right button pressed     (CX | 08H)
                  bit 4 = right button released    (CX | 10H)
                  bit 5 = center button pressed    (CX | 20H)
                  bit 6 = center button released   (CX | 40H)
                  All events:      CX = 007fH
          ES:DX address of your event handler code
 Returns: CX    event mask of previous event handler
          ES:DX address of the previously-installed event handler code
    Info: This function works like INT 33H 000cH (which see for details).
          The only difference is that upon return, you obtain the address
          and event mask of the previously-installed event handler.

          This provides a way to install an event handler temporarily; that
          is, you can install one while performing a certain subroutine,
          then restore the previous one when you exit that subroutine.

          This also provides a way to chain event handlers.  Install a
          handler for all events, and if you get an event which you don't
          really care about, pass it on to the previously-installed handler
          (assuming its event mask shows that it expects the event).

   Notes: INT 33H 0018H provides a flexible means for installing up to
          three specialized-event handlers.

See Also: INT 33H: Mouse Support
          Interrupts and BIOS Services