Publish Rust crate & WASM support

Due to the Electrum dependency, it's likely the Rust crate can't be cross-compiled to WASM for web environments. The BDK approach to solving this is to use the bdk_esplora crate.

Also, I noticed that the Rust crates are unpublished, which means that any libraries depending on Rust GDK wouldn't also be able to be published.