MBitmapWindow [(]SourceBitmap.w,DestBitmap.w,X.w,Y.w,Width.w,Height.w[)] ; Cludge Bitmap within a Bitmap

Makes a new chunky Bitmap object based on an existing chunky Bitmap object,
allowing a `window' within the exising Bitmap to be used as the new one.
Therefore graphics and sencil data are cludged from the existing Bitmap's data.
Width should be a multiple of 4 and X,Y specify the top-left corner of the window
within the existing chunky Bitmap. If used as a function, this command will
return the address of the Bitmap's graphics data, or 0 for failure.