Function:   GRINIT( <expN1>, <expN2> ) --> NIL

Synopsis:   Sets maximal X,Y coordinates for Graphics Screens

            Call this function whenever You want to set the maximal
            x,y screen coordinates to any other values than the
            ones set by the UTINIT() function.

            The globals  b_maxx  and  b_maxy  are set according
            to what Your system allows at maximum.

            If Your video card supports 800 x 600 pixels, call this
            function with:
                              GRINIT( 800, 600 )

            setting the maximal x,y coordinates to this value to
            benefit from the provided Graphics functions

Examples:   GRINIT( 800,600 )    && set maximal x,y coordinates to 800x600
            GRINIT( 640,480 )    &&    "  "     "      "      640x480

Returns:    Nothing