INT 21 - DOS 1+ - WRITE CHARACTER TO STANDARD OUTPUT
        AH = 02h
        DL = character to write
Return: AL = last character output (despite the official docs which state
                nothing is returned) (at least DOS 3.3-5.0)
Notes:   Break are checked, and INT 23 executed if pressed
        standard output is always the screen under DOS 1.x, but may be
          redirected under DOS 2+
        the last character output will be the character in DL unless DL=09h
          on entry, in which case AL=20h as tabs are expanded to blanks
SeeAlso: AH=09h