MTile16x16 [ShapeNumber.w,]Xpos.w,Ypos.w ; Block-blit 16x16 shape to bitmap, size must be 16x16, align x/y

Performs a highly optimised blit of the currently-used or specified chunky Shape
into the currently used chunky Bitmap at Xpos,Ypos. The Shape should be 16x16 in
size and *both* Xpos and Ypos should be multiples of 16.