* fix: use a 'static lifetime for the web backend's `Event` types
* implement hidpi for stdweb (web-sys wip?)
* fix: make all canvas resizes go through backend::set_canvas_size
* update Window docs for web, make `inner/outer_position` return the position in the viewport
* Begin implementing DPI generics
* Fix multithreaded example
* Format
* Fix serde test
* hopefully fix most of the errors
* Fix dpi module errors
* More error fixings
* Format
* fix macos errors
* Another error pass
* Replace bad type signatures
* more fixins
Adds fullscreen using native web APIs to the stdweb and web-sys backends.
Due to limitations of browser APIs, requests for fullscreen can only be fulfilled during a short-lived user-triggered event. This commit does automatically handle that under the hood, but it does introduce unavoidable latency in full-screening the canvas.
