Builds a vocabulary object based on the tokens in the input.

        Args:
            sents: A list of lists of tokens (representing sentences)

        Vocab kwargs include:
            max_size
            min_freq
            specials
            unk_init

def fit(self, sents, **kwargs):
        """Builds a vocabulary object based on the tokens in the input.

        Args:
            sents: A list of lists of tokens (representing sentences)

        Vocab kwargs include:
            max_size
            min_freq
            specials
            unk_init
        """
        tokens = list(itertools.chain.from_iterable(sents))
        counter = Counter(tokens)
        self.vocab = self.build_vocab(counter, **kwargs)