INT 21 - DOS 1+ - READ CHARACTER FROM STANDARD INPUT, WITH ECHO
        AH = 01h
Return: AL = character read
Notes:   Break are checked, and INT 23 executed if read
        character is echoed to standard output
        standard input is always the keyboard and standard output the screen
          under DOS 1.x, but they may be redirected under DOS 2+
SeeAlso: AH=07h,AH=08h,AH=0Ah