INT 16 - KEYBOARD - GET SHIFT FLAGS
        AH = 02h
Return: AL = shift flags
            bit 7: Insert active
                6: CapsLock active
                5: NumLock active
                4: ScrollLock active
                3: Alt key pressed (either Alt on 101/102-key keyboards)
                2: Ctrl key pressed (either Ctrl on 101/102-key keyboards)
                1: left shift key pressed
                0: right shift key pressed
SeeAlso: AH=22h,INT 18/AH=02h