message: [tf.data] Improve documentation for `Dataset.batch()` wrt. small final batches.
  This partially addresses the concerns in issue
diff: @@ -724,6 +724,12 @@ class Dataset(object):
  def batch(self, batch_size):
  """Combines consecutive elements of this dataset into batches.
  + NOTE: If the number of elements (`N`) in this dataset is not an exact
  + multiple of `batch_size`, the final batch contain smaller tensors with
  + shape `N % batch_size` in the batch dimension. If your program depends on
  + the batches having the same shape, consider using the
  + @{tf.contrib.data.batch_and_drop_remainder} transformation instead.
  +
  Args:
  batch_size: A `tf.int64` scalar `tf.Tensor`, representing the number of
  consecutive elements of this dataset to combine in a single batch.
  