MBoxF Xpos.w,Ypos.w,Xpos2.w,Ypos2.w[,Colour] Draw a filled box in a bitmap [to specified colour]

Fills the specified area within the currently used chunky Bitmap to the currently
used ink colour or the specified colour. Width of the box does NOT have to be a
multiple of 4 and the box should be at least 1x1 in size. The specified area
 should fit within the dimensions of the Bitmap, and it is possible for X2,Y2 to
be further left and/or further up the screen than X1,Y1. See also MDrawingMode
for further details of the drawing modes that are available.