code: private Func1<SoundCloudUser, SoundCloudUser> cacheArtistProfile() {
          return new Func1<SoundCloudUser, SoundCloudUser>() {
              @Override
              public SoundCloudUser call(SoundCloudUser soundCloudUser) {
                  mCacheRam.artistProfile = soundCloudUser;
                  return soundCloudUser;
              }
          };
      }
docs: "Cache" the artist profile retrieved from network in RAM
  to avoid requesting SoundCloud API for next call.
  
  @return {@link rx.functions.Func1} used to save the retrieved artist