Use web-sys for web backend (#444)

A small step for #446 🕸️ Web support, use web-sys to interface to the web.
Previously, we would try to use glutin on the web, which is not supported;
now glutin is only used on native: fixes #171 could not find Context in platform_impl.

winit is still used on both, but the GL context is created with web-sys and glow
(on the web), and created with glutin and used with glow (on native). stdweb is
no longer used, being replaced by web-sys.

Substantial refactoring to allow reusing the code between web/native:

* settings: use VirtualKeyCode from winit, not reexported from glutin
* std_or_web: remove broken localstoragefs/stdweb, add File placeholder
* render: disable skin_thread on wasm since we don't have threads

* gl: use glow types in gl wrapper (integers in native, but Web*Key in web)
* gl: web-sys WebGlUniformLocation does not implement Copy trait, so glow::UniformLocation doesn't so gl::Uniform can't
* gl: refactor context initialization, pass glow::Context to gl::init for consistency between native/web
* gl: update to glow with panicking tex_image_2d_multisample web-sys wrapper

* glsl: use shader version in GLSL for WebGL 2 and OpenGL 3.2

* shaders: add explicit float/int type conversions, required for WebGL
* shaders: specify mediump precision, required for WebGL
* shaders: specify fragment shader output locations for WebGL

* main: refactor handle_window_event to take a winit window, not glutin context
* main: handle resize outside of handle_window_event since it updates the glutin window (the only event which does this)
* main: use winit events in handle_window_event not reexported glutin events
* main: refactor game loop handling into tick_all()
* main: create winit window for WebGL, and use winit_window from glutin
* main: restore console_error_panic_hook,  mistakingly removed in (#260)
* main: remove force setting env RUST_BACKTRACE=1, no longer can set env on web

* www: index.js: fix wasm import path
* www: npm update, npm audit fix
* www: update readme to link to status on #446 🕸️ Web support

Cargo.toml

@@ -20,8 +20,8 @@ opt-level = 1
 [dependencies]
 cfg-if = "1.0.0"
 wasm-bindgen = "0.2.69"
-glutin = "0.26.0"
-glow = { git = "https://github.com/iceiix/glow", rev = "45c808678735e03737d5e1b9d6ed0e21070edcd9" }
+winit = { version = "0.24.0", features = [ "web-sys" ]}
+glow = { git = "https://github.com/iceiix/glow", rev = "b354346dee69ff0ca7ccef67f7580dfbb697423b" }
 byteorder = "1.3.4"
 serde = "1.0.118"
 serde_json = "1.0.60"
@@ -42,10 +42,11 @@ clipboard = "0.5.0"
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 reqwest = { version = "0.10.10", features = [ "blocking" ]}
+glutin = "0.26.0"
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
-stdweb = "0.4.20"
-winit = { version = "0.24.0", features = [ "stdweb" ]}
+console_error_panic_hook = "0.1.6"
+web-sys = "0.3.46"
 
 [dependencies.steven_resources]
 path = "./resources"