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

tests/serde_objects.rs

@@ -3,8 +3,8 @@
 extern crate serde;
 extern crate winit;
 
-use winit::{ControlFlow, MouseCursor};
-use winit::{
+use winit::window::{MouseCursor};
+use winit::event::{
     KeyboardInput, TouchPhase, ElementState, MouseButton, MouseScrollDelta, VirtualKeyCode,
     ModifiersState
 };
@@ -14,8 +14,7 @@ use serde::{Serialize, Deserialize};
 fn needs_serde<S: Serialize + Deserialize<'static>>() {}
 
 #[test]
-fn root_serde() {
-    needs_serde::<ControlFlow>();
+fn window_serde() {
     needs_serde::<MouseCursor>();
 }