Event Loop 2.0 API and Windows implementation (#638)

* Rename EventsLoop and associated types to EventLoop

* Rename WindowEvent::Refresh to WindowEvent::Redraw

* Remove second thread from win32 backend

* Update run_forever to hijack thread

* Replace windows Mutex with parking_lot Mutex

* Implement new ControlFlow and associated events

* Add StartCause::Init support, timer example

* Add ability to send custom user events

* Fully invert windows control flow so win32 calls into winit's callback

* Add request_redraw

* Rename platform to platform_impl

* Rename os to platform, add Ext trait postfixes

* Add platform::desktop module with EventLoopExt::run_return

* Re-organize into module structure

* Improve documentation

* Small changes to examples

* Improve docs for run and run_return

* Change instances of "events_loop" to "event_loop"

* Rename MonitorId to MonitorHandle

* Add CHANGELOG entry

* Improve WaitUntil timer precision

* When SendEvent is called during event closure, buffer events

* Fix resize lag when waiting in some situations

* Update send test and errors that broke some examples/APIs

* Improve clarity/fix typos in docs

* Fix unreachable panic after setting ControlFlow to Poll during some RedrawRequested events.

* Fix crash when running in release mode

* Remove crossbeam dependency and make drop events work again

* Remove serde implementations from ControlFlow

* Fix 1.24.1 build

* Fix freeze when setting decorations

* Replace &EventLoop in callback with &EventLoopWindowTarget

* Document and implement Debug for EventLoopWindowTarget

* Fix some deadlocks that could occur when changing window state

* Fix thread executor not executing closure when called from non-loop thread

* Fix buffered events not getting dispatched

* Fix crash with runner refcell not getting dropped

* Address review feedback

* Fix CHANGELOG typo

* Catch panics in user callback

src/platform_impl/macos/mod.rs

@@ -0,0 +1,51 @@
+#![cfg(target_os = "macos")]
+
+pub use self::event_loop::{EventLoop, Proxy as EventLoopProxy};
+pub use self::monitor::MonitorHandle;
+pub use self::window::{Id as WindowId, PlatformSpecificWindowBuilderAttributes, Window2};
+use std::sync::Arc;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct DeviceId;
+
+impl DeviceId {
+    pub unsafe fn dummy() -> Self {
+        DeviceId
+    }
+}
+
+use {CreationError};
+
+pub struct Window {
+    pub window: Arc<Window2>,
+}
+
+impl ::std::ops::Deref for Window {
+    type Target = Window2;
+    #[inline]
+    fn deref(&self) -> &Window2 {
+        &*self.window
+    }
+}
+
+impl Window {
+
+    pub fn new(event_loop: &EventLoop,
+               attributes: ::WindowAttributes,
+               pl_attribs: PlatformSpecificWindowBuilderAttributes) -> Result<Self, CreationError>
+    {
+        let weak_shared = Arc::downgrade(&event_loop.shared);
+        let window = Arc::new(try!(Window2::new(weak_shared, attributes, pl_attribs)));
+        let weak_window = Arc::downgrade(&window);
+        event_loop.shared.windows.lock().unwrap().push(weak_window);
+        Ok(Window { window: window })
+    }
+
+}
+
+mod event_loop;
+mod ffi;
+mod monitor;
+mod util;
+mod view;
+mod window;