* Expose all fields of recent protobufs
* Add support for user-scoped playlists, user root playlists and
playlist annotations
* Convert messages with the Rust type system
* Attempt to adhere to embargos (tracks and episodes scheduled for
future release)
* Return `Result`s with meaningful errors instead of panicking on
`unwrap`s
* Add foundation for future playlist editing
* Up version in connection handshake to get all version-gated features
- perf:
* base62 encoding is an order of magnitude faster (~20x);
* base16/62 enc/dec and from_uri are several times faster (~2-20x);
* Let FileId::to_base16() reuse the hex encoder (~20x);
- changes:
* Add to_uri() method;
* Make from_uri() error handling consistent;
* Move audio type from string matching to a SpotifyAudioType factory (private);
* Implent From/Into<&str> for SpotifyAudioType;
* Add representation sizes as associated constants (private);
- cs/docs:
* Add rudimentary docs for most public funcs;
* Add trivial test cases for the codecs;
