Release Alpha 4

[Osspial]

I'd like to get #1168, #1171, #1175, #1180, #1186, and possibly #1121 in before this releases, but most of those PRs seem close to getting merged so that shouldn't be too much of a hassle.

• Update release date in CHANGELOG
• Fix panic upon closing the app on iOS #1168
• Improve interaction between fullscreen windows and monitor-switching keyboard shortcuts #1171
• Always dispatch a RedrawRequested event after creating a new window #1175
• Wayland support for set_cursor_grab and set_cursor_visible #1180
• Prevent EventLoop from getting initialized outside the main thread in cross-platform functions #1186
• Defer window creation until UIApplicationMain on iOS #1121

[ghost]

We should wait on #1121 until a new Simulator runtime is released to see if this was fixed by Apple or if we still need to address this in winit. See #1120 (comment).