Implement Windowed Fullscreen

There are two kinds of fullscreen. One where you take over the whole
output the other where you just set the window size to the screen
size and get rid of decorations. The first one already existed,
implement the second which is more common for normal desktop apps.
Use an enum to consolidate all the fullscreen states.

src/platform/linux/wayland/context.rs

@@ -359,6 +359,12 @@ pub struct MonitorId {
     ctxt: Arc<WaylandContext>
 }
 
+impl PartialEq for MonitorId {
+    fn eq(&self, other: &MonitorId) -> bool {
+        self.id == other.id
+    }
+}
+
 impl MonitorId {
     pub fn get_name(&self) -> Option<String> {
         let mut guard = self.ctxt.evq.lock().unwrap();

src/platform/linux/wayland/window.rs

@@ -54,7 +54,7 @@ impl Window {
                 *(decorated.handler()) = Some(DecoratedHandler::new());
 
                 // set fullscreen if necessary
-                if let Some(PlatformMonitorId::Wayland(ref monitor_id)) = attributes.monitor {
+                if let Some(PlatformMonitorId::Wayland(ref monitor_id)) = attributes.fullscreen.get_monitor() {
                     ctxt.with_output(monitor_id.clone(), |output| {
                         decorated.set_fullscreen(Some(output))
                     });