Initial stages of mercury (metadata) caching
Working (messy) mercury cache, needs to be restructured/cleaned up
Split hermes requests/caching into the 'spotify.hermes' module
Fixed bug in HermesCache.get
Fixed bug in HermesRequest.update_response, renamed some HermesCache functions
Playlists now work with HermesRequest
Fixed bug when returning cached items
Merge branch 'feature/mercury-cache' into develop