Events loop backend (#269)

* Don't use UNIX_BACKEND in Window2::new

* Move get_available_monitors and get_primary_monitor to EventsLoop

* Remove UNIX_BACKEND

* Restore choosing the Linux backend

* Return a XNotSupported for new_x11()

* Fix fullscreen example

src/platform/linux/wayland/event_loop.rs

@@ -131,6 +131,11 @@ impl EventsLoop {
         }
     }
 
+    #[inline]
+    pub fn context(&self) -> &Arc<WaylandContext> {
+        &self.ctxt
+    }
+
     pub fn create_proxy(&self) -> EventsLoopProxy {
         EventsLoopProxy {
             ctxt: Arc::downgrade(&self.ctxt),