Compile to WebAssembly

[FZambia]

Relates #67

This pull requests adds possibility to use centrifuge-go in browser using compilation to WebAssembly. The implementation here is an adapted code from https://github.com/nhooyr/websocket which supports WASM env for some time already. PR contains a simple example that demonstrates how centrifuge-go and wasm can be used together to build a browser app.

The example shown in the PR weights 12 MB when using standard Go compiler. Which is quite sad. And this makes me skeptical a bit about the idea - not sure whether someone wants to put file of this size to the browser app.

For Tinygo the situation is quite bad at the moment:

1. We can't use segmentio/encoding package - github.com/segmentio/encoding@v0.3.5/json/reflect.go:12:23: ArrayOf not declared by package reflect - may be fixed by switching to stdlib JSON and using build tags in protocol package or when mapstructure requires MapOf and friends tinygo-org/tinygo#2115 solved
2. Tinygo does not support (reflect.Type).PkgPath() - Implement the PkgPath() method on reflect.Type tinygo-org/tinygo#2668
3. Tinygo does not implement timers runtime timers are unimplemented tinygo-org/tinygo#1037 - Uncaught (in promise) LinkError: WebAssembly.instantiate(): Import #13 module="env" function="time.stopTimer" error: function import requires a callable

Tinygo could help reduce 12 MB to ~3 MB when all the issues mentioned above solved.