mouse demo redraw screen on window resize

tools/cmd/mouse_demo/main.go

@@ -67,6 +67,7 @@ func Run(args []string) (rc int, err error) {
 		lp.AllowLineWrapping(false)
 		defer lp.AllowLineWrapping(true)
 		if current_mouse_event == nil {
+			lp.ClearScreen()
 			lp.Println(`Move the mouse or click to see mouse events`)
 			return
 		}
@@ -150,6 +151,10 @@ func Run(args []string) (rc int, err error) {
 		}
 		return nil
 	}
+	lp.OnResize = func(old_size loop.ScreenSize, new_size loop.ScreenSize) error {
+		draw_screen()
+		return nil
+	}
 	err = lp.Run()
 	if err != nil {
 		rc = 1