Returns a set of all tokens occuring the evaluation datasets.

def get_analogy_task_tokens(args):
    """Returns a set of all tokens occuring the evaluation datasets."""
    tokens = set()
    for _, _, dataset in iterate_analogy_datasets(args):
        tokens.update(
            itertools.chain.from_iterable(
                (d[0], d[1], d[2], d[3]) for d in dataset))
    return tokens