Feature request: add radio stations

[robfreundlich]

I'm a user of Google Play Music Desktop Player, which uses your library to expose an API to control it. lately, I've been getting a lot of mileage from creating my own radio stations from my playlists. Because of that, it'd be great to be able to list and play those stations via GPMDP's API.

Would you please consider adding a RadioStation namespace with the ability to list and play to your library? Adding a "start Radio Station" to the Playlist namespace would be nice too, but would be (as a mentor of mine used to say of stretch goals) "optional extra credit".