Support for audiobooks

[chyron8472]

@chyron8472

You should add Musicbrainz (or something similar) as an agent.

Oh, my God. They listened to me.

https://forums.plex.tv/t/upgrading-plex-music-libraries/469659

@PlexInfo

Upgraded music in Plex starts with the best-in-class database of music content from MusicBrainz and then also adds in the best-in-class musical metadata from AllMusic .