INT 21 - DOS 1+ - DIRECT CONSOLE OUTPUT
        AH = 06h
        DL = character (except FFh)
Return: AL = character output (despite official docs which state nothing is
                returned) (at least DOS 3.3-5.0)
Notes:  does not check  Break
        writes to standard output, which is always the screen under DOS 1.x,
          but may be redirected under DOS 2+
SeeAlso: AH=09h