To turn any struct into a composite element, you can implement a render method
with the following signature:
fn render<V: View>(&mut self, view: &mut V, cx: &mut ViewContext<V>) -> AnyElement<V>;
Then add #[derive(Element)] to the struct definition.
This will make it easier to introduce higher-level components that are expressed in
terms of other elements.
Nathan Sobo
bede668b14