Expose light client verifier to JavaScript

[romac]

See: #463

Basic prototype that exposes the verifier to JS via wasm-pack/wasm-bindgen.

Rust wrapper: https://github.com/informalsystems/tendermint-rs/blob/romac/wasm-verifier/wasm-client/src/lib.rs
Usage from JS: https://github.com/informalsystems/tendermint-rs/blob/romac/wasm-verifier/wasm-client/app/index.js

To make this work, one currently has to:

1. Run wasm-pack build from within the wasm-client folder
2. Move the app directory and run npm start
3. Open http://localhost:8080/ and look at the console
4. It should display:

{
  "Ok": {
    "Invalid": {
      "NotWithinTrustPeriod": {
        "expires_at": "1970-01-15T00:00:03Z",
        "now": "2020-10-21T12:40:04.160328400Z"
      }
    }
  }
}

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG.md

[webmaster128]

Thank you! Some first thoughts here

[webmaster128]

Regarding the empty file above: As far as I know, .cargo-ok can be deleted.

[webmaster128]

Suggestion: rename to something like "js-verifier" or "light-client-js" because wasm-bindgen binds to JS only.

[webmaster128]

Should not be needed since there is a LICENSE in the repo root

[webmaster128]

Should not be needed since there is a LICENSE in the repo root

[webmaster128]

license entry here would be nice

[webmaster128]

I think this file is not needed

[webmaster128]

Should not be needed since there is a LICENSE in the repo root

[webmaster128]

Should not be needed since there is a LICENSE in the repo root

[webmaster128]

Suggested change

	"author": "Ashley Williams <ashley666ashley@gmail.com>",
	"contributors": ["Romain Ruetschi <romain@informal.systems>"],

[cargo-dep-bot]

This PR made the following dependency changes:

Added Packages (Duplicate versions in '()'):
	bumpalo 3.4.0
	console_error_panic_hook 0.1.6
	js-sys 0.3.46
	scoped-tls 1.0.0
	wasm-bindgen 0.2.69
	wasm-bindgen-backend 0.2.69
	wasm-bindgen-futures 0.4.19
	wasm-bindgen-macro 0.2.69
	wasm-bindgen-macro-support 0.2.69
	wasm-bindgen-shared 0.2.69
	wasm-bindgen-test 0.3.19
	wasm-bindgen-test-macro 0.3.19
	wasm-client 0.1.0
	web-sys 0.3.46