Fill the windows in the examples with a solid color

Fixes #776.

examples/theme.rs

@@ -8,6 +8,9 @@ use winit::{
     window::{Theme, WindowBuilder},
 };
 
+#[path = "util/fill.rs"]
+mod fill;
+
 fn main() {
     SimpleLogger::new().init().unwrap();
     let event_loop = EventLoop::new();
@@ -66,6 +69,10 @@ fn main() {
                 }
                 _ => (),
             },
+            Event::RedrawRequested(_) => {
+                println!("\nredrawing!\n");
+                fill::fill_window(&window);
+            }
             _ => (),
         }
     });