Create and select a virtual screen.
n = Virtual screen number (0 - 7).
t = Type of screen (0 = text, 1 = graphics).
x = Horizontal position of left corner (0 - 39 or 31).
y = Vertical position of top corner (0 - 23).
w = Width of virtual screen (x + w <= 40 or 32).
h = Height of virtual screen (y + h <= 24).
s = Physical screen width (40 or 32).
Include file: mtxscrn.h