Adds a painted rectangle to the current page. The rectangle
location and size is determined by the current rectangle, the fill color is
determined by the current color and any options are
determined by the current options.
By specifying values for the horizontal and vertical radius
parameters you can draw rectangles with rounded corners. The values
refer to the radii of the ellipse used to draw the corners.
By setting the horizontal radius parameter to half the width of
the rect and the vertical radius parameter to half the height of
the rect you can draw filled ovals and circles.
The FillRect function returns the Object ID of the newly added