Wasm/web proof of concept

[sneurlax]

Rust on the web via Wasm in Typescript should be proven as a concept.

Target wasm32-unknown-wasi or wasm32-unknown-emscripten

wasm32-unknown-unknown is probably blocked by tokio, see:

• Enabling time causes panic on wasm32-unknown-unknown target tokio-rs/tokio#5418
• Support Webassembly tokio-rs/tokio#1597
• https://docs.rs/tokio/latest/tokio/#wasm-support

See the related issue for Dart consumers: ManyMath/monero-rust#2

[sneurlax]

We will probably not be able to use wasm-pack/wasm-bindgen: rustwasm/wasm-bindgen#3421