MBlit [ShapeNumber.w,]Xpos.w,Ypos,w ; Blit shape to bitmap, any coords

Performs a straight masked-blit of a chunky Shape into a chunky Bitmap to
coordinates Xpos,Ypos. If the ShapeNumber is omitted the currently used Shape is
used. The type of blit performed is defined with the MBlitMode command. Normally
the Shape is simply cookie-blitted onto the Bitmap, with areas of Colour 0 as
transparent. If the Shape does not have a cookie, it will be blitted in unmasked
`Replace' mode.