This tracks resizes separately, and synthesizes them for the event iterators as needed, so that OS X apps don't generate a whole set of resize events after each resize.
These events are batched, and delievered en masse at the end of the resize. This isn't a great developer experience (and it should probably be called out in the docs), but it makes it possible for winit client applications to detect and respond to resizes without special-casing Mac OS targets.
See #39. This is only a partial fix, and does not provide on-the-fly resize events.
This fixes propagation of Event::Awakend from wakeup_event_loop() when
using poll_event() on macOS.
Currently wait_event() translates all unknown events into
Event::Awakened so doesn't need the explicit translation.
