sized widgets!

src/core/rect.rs

@@ -28,7 +28,7 @@ impl Rect {
 }
 
 impl Widget for Rect {
-    fn draw(&self, painter: &mut Painter) {
+    fn draw(&mut self, painter: &mut Painter) {
         painter.write(RectPrimitive {
             color: self.color,
             radius: self.radius,