Fill the windows in the examples with a solid color

Fixes #776.

examples/fullscreen.rs

@@ -9,6 +9,9 @@ use winit::window::{Fullscreen, WindowBuilder};
 #[cfg(target_os = "macos")]
 use winit::platform::macos::WindowExtMacOS;
 
+#[path = "util/fill.rs"]
+mod fill;
+
 fn main() {
     SimpleLogger::new().init().unwrap();
     let event_loop = EventLoop::new();
@@ -123,6 +126,9 @@ fn main() {
                 },
                 _ => (),
             },
+            Event::RedrawRequested(_) => {
+                fill::fill_window(&window);
+            }
             _ => {}
         }
     });