Libre.fm support

[jaduncan]

I'd be really interested in getting this to work with libre.fm, but I see you're considering a broad rewrite. Do you want a PR or for me to wait until the refactor?

[taurheim]

@jaduncan let me know if you're still using libre.fm. I've added support for listenbrainz, I'm not sure if people are still using libre.fm as their primary data source?