Create a Batch directly from a number of Variables.

def fromvars(cls, dataset, batch_size, train=None, **kwargs):
        """Create a Batch directly from a number of Variables."""
        batch = cls()
        batch.batch_size = batch_size
        batch.dataset = dataset
        batch.fields = dataset.fields.keys()
        for k, v in kwargs.items():
            setattr(batch, k, v)
        return batch