Renamed Descriptor 'from_dict' to 'from_node_dict', added '$source' key to dict
Initial support for collections
Fixed bug when returning multiple items from a collection
Added support for collection artist portraits and fixed bug when there is no image available
Fixed issue with 'on_close' requested disconnects
Spotify.connect - re-authenticate if not already authenticated
Implemented Artist.top_tracks
Merge branch 'feature/collections' into develop
Implemented Playlist.image