- Derive `Default` trait for the vec / hashmap wrapper types in
`librespot-metadata`
- The wrapped types (`Vec` / `Hashmap`) implement Default, so the
wrapper types should as well
* 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
