GooCanvasRect represents a rectangle item.
It is a subclass of CanvasItemSimple and so inherits all of the style properties such as "stroke-color", "fill-color" and "line-width".
It also implements the CanvasItem interface, so you can use the CanvasItem functions such as raise and rotate.
To create a CanvasRect use create.
To get or set the properties of an existing CanvasRect, use @get and @set.