Write string (AT,XT286,PS,EGA,VGA)

        AH = 13h
        AL = mode
            bit 0: set in order to move cursor after write
            bit 1: set if string contains alternating characters and attributes
        BL = attribute if AL bit 1 clear
        BH = display page number
        DH,DL = row,column of starting cursor position
        CX = length of string
        ES:BP = pointer to start of string