create_zbuffer - Creates a Z-buffer for a bitmap. Allegro game programming
ZBUFFER *create_zbuffer(BITMAP *bmp);
Creates a Z-buffer using the size of the BITMAP you are planning to draw on.
Several Z-buffers can be defined but only one can be used at the same time, so
you must call set_zbuffer() to make this Z-buffer active.
Returns the pointer to the ZBUFFER or NULL if there was an error. Remember to
destroy the ZBUFFER once you are done with it, to avoid having memory leaks.