INT 50 - Vanderaart TEXT WINDOWS - OUTPUT LINE TO WINDOW
        AX = 0003h
        ES:BX -> text string
        CX = string length (0000h if ASCIZ string)
        DL = position (FFh centered, else flush left)
        DH = starting row
        DI = window handle
Return: AX = status
            0000h successful
            FFFFh did not fit in window