Get the song collection of a user.

        :param user_id: ID of a user.
        :rtype: list of :class:`Song`

def collection(self, user_id):
        """
        Get the song collection of a user.

        :param user_id: ID of a user.
        :rtype: list of :class:`Song`
        """
        # TODO further evaluation of the page param, I don't know where the
        # limit is.
        dct = {'userID': user_id, 'page': 0}
        r = 'userGetSongsInLibrary'
        result = self.connection.request(r, dct, self.connection.header(r))
        songs = result[1]['Songs']
        return [Song.from_response(song, self.connection) for song in songs]