Write characters (not attr.) at cursor position

        Entry:
          AH = 0Ah
          AL = character
          BH = display page - alpha mode
          BL = color of character (graphics mode)
          CX = number of times to write character
                 (EGA) in graphics modes, replication count in CX works
                 correctly
               only if all character written are contains on the same row
        Return:
          AX,SI,DI,BP destroyed by call