Introduce Widget::overlay 🎉

graphics/src/renderer.rs

@@ -62,7 +62,7 @@ where
     fn explain<Message>(
         &mut self,
         defaults: &Defaults,
-        widget: &dyn Widget<Message, Self>,
+        widget: &dyn Widget<'_, Message, Self>,
         layout: Layout<'_>,
         cursor_position: Point,
         color: Color,

graphics/src/widget/canvas.rs

@@ -134,7 +134,7 @@ impl<Message, P: Program<Message>> Canvas<Message, P> {
     }
 }
 
-impl<Message, P, B> Widget<Message, Renderer<B>> for Canvas<Message, P>
+impl<'a, Message, P, B> Widget<'a, Message, Renderer<B>> for Canvas<Message, P>
 where
     P: Program<Message>,
     B: Backend,