code: def add(options = {})
        assert_valid_keys(options, :playlist, :index)
        options = {:playlist => playlist.id, :index => 0}.merge(options)
  
        # Create a copy of the song so that the playlist can get set properly
        song = dup
        song.attributes = {:playlist => options[:playlist]}
        playlist, index = song.playlist, options[:index]
  
        api('playlist.add', :playlist_name => playlist.id, :song_dict => {:fileid => id}, :index => index)
        playlist.songs.insert(index, song) if playlist.loaded?
        true
      end
docs: Adds the song to one of the user's playlists.
  
   @param [Hash] options The options for where to add the song
   @option options [String] :playlist ("default") The playlist to add the song in
   @option options [Fixnum] :index (0) The location in the playlist to insert the song
   @return [true]
   @raise [ArgumentError] if an invalid option is specified
   @raise [Turntabler::Error] if the command fails
   @example
     song.add(:index => 1)   # => true