Begin the widgetization

src/ui.rs

@@ -4,6 +4,7 @@ mod list;
 mod room;
 mod rooms;
 mod util;
+mod widget;
 
 use std::sync::{Arc, Weak};
 use std::time::Duration;

src/ui/widget.rs

@@ -0,0 +1,9 @@
+use async_trait::async_trait;
+use toss::frame::{Frame, Pos, Size};
+
+#[async_trait]
+pub trait Widget {
+    fn size(max_width: Option<u16>, max_height: Option<u16>) -> Size;
+
+    async fn render(frame: &mut Frame, pos: Pos, size: Size);
+}