Rust docs

[clehner]

Document public API

• https://docs.rs/didkit/
• https://docs.rs/didkit-cli/
• https://docs.rs/didkit-http/

Reference: https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html

• ssi rustdocs: Rustdocs ssi#331
• didkit crate
  • front-page, features
  • c module (partially documented already)
  • error module
  • jni module
  • runtime module
  • ssh_agent module
  • DID_METHODS struct
• didkit-cli crate
  • Expand CLI help text (DIDKit enum - Improve rustdocs ssi#311 (comment)); figure out why this is not appearing on docs.rs
    • Improve key-to-did description (Add description for method-pattern CLI argument #217 (comment)): Update key-to-did #238
• didkit-http crate