Replace listenbrainz-rust library with listenbrainz

[InputUsername]

listenbrainz-rust depends on reqwest and therefore pulls in a bunch of crates from the async/tokio ecosystem for no reason. I've written listenbrainz, which uses ureq, bringing in significantly fewer dependencies.

I have already attempted to port rescrobbled over to listenbrainz, but it seems to randomly error sometimes when submitting songs or authenticating. Need to investigate.

[InputUsername]

Implemented in v0.5.0.