MBitmap [(]BitmapNumber.w,Width.w,Height.w[)] ; Allocmem for bitmap data

Initialises a new bitmap, which basically means that is creates a new chunky
Bitmap object. If Mildred's autostencil feature is turned on, a stencil for the
bitmap will also be initialised. Width should be a multiple of 4 but bear in mind
that if you use any of the `Block' or `Tile' commands on 040+ it is necessary to
have a Bitmap width in multiples of 16. A chunky Bitmap object contains graphics
data (also stencil-data). Unlike normal blitz bitmap's, a chunky Bitmap in Mildred
has stencils as integral parts of the object in the same way that shapes have
integral cookies. If used as a function, this command will return the address of
the new Bitmap's graphics data or 0 for failure.