v0.20.0-alpha4

• Add web support via the 'stdweb' or 'web-sys' features
• On Windows, implemented function to get HINSTANCE
• On macOS, implement run_return.
• On iOS, fix inverted parameter in set_prefers_home_indicator_hidden.
• On X11, performance is improved when rapidly calling Window::set_cursor_icon.
• On iOS, fix improper msg_send usage that was UB and/or would break if ! is stabilized.
• On Windows, unset maximized when manually changing the window's position or size.
• On Windows, add touch pressure information for touch events.
• On macOS, differentiate between CursorIcon::Grab and CursorIcon::Grabbing.
• On Wayland, fix event processing sometimes stalling when using OpenGL with vsync.
• Officially remove the Emscripten backend.
• On Windows, fix handling of surrogate pairs when dispatching ReceivedCharacter.
• On macOS 10.15, fix freeze upon exiting exclusive fullscreen mode.
• On iOS, fix panic upon closing the app.
• On X11, allow setting mulitple XWindowTypes.
• On iOS, fix null window on initial HiDpiFactorChanged event.
• On Windows, fix fullscreen window shrinking upon getting restored to a normal window.
• On macOS, fix events not being emitted during modal loops, such as when windows are being resized
  by the user.
• On Windows, fix hovering the mouse over the active window creating an endless stream of CursorMoved events.
• Always dispatch a RedrawRequested event after creating a new window.
• On X11, return dummy monitor data to avoid panicking when no monitors exist.
• On X11, prevent stealing input focus when creating a new window.
  Only steal input focus when entering fullscreen mode.
• On Wayland, fixed DeviceEvents for relative mouse movement is not always produced
• On Wayland, add support for set_cursor_visible and set_cursor_grab.
• On Wayland, fixed DeviceEvents for relative mouse movement is not always produced.
• Removed derivative crate dependency.
• On Wayland, add support for set_cursor_icon.
• Use impl Iterator<Item = MonitorHandle> instead of AvailableMonitorsIter consistently.
• On macOS, fix fullscreen state being updated after entering fullscreen instead of before,
  resulting in Window::fullscreen returning the old state in Resized events instead of
  reflecting the new fullscreen state
• On X11, fix use-after-free during window creation
• On Windows, disable monitor change keyboard shortcut while in exclusive fullscreen.
• On Windows, ensure that changing a borderless fullscreen window's monitor via keyboard shortcuts keeps the window fullscreen on the new monitor.
• Prevent EventLoop::new and EventLoop::with_user_event from getting called outside the main thread.
  • This is because some platforms cannot run the event loop outside the main thread. Preventing this
    reduces the potential for cross-platform compatibility gotchyas.
• On Windows and Linux X11/Wayland, add platform-specific functions for creating an EventLoop outside the main thread.
• On Wayland, drop resize events identical to the current window size.
• On Windows, fix window rectangle not getting set correctly on high-DPI systems.