message: Fix the api docstrings for `on_*_batch_begin` methods in `callbacks.Callback`
  class.
diff: @@ -665,8 +665,9 @@ class Callback(object):
  Arguments:
  batch: Integer, index of batch within the current epoch.
  - logs: Dict. Has keys `batch` and `size` representing the current batch
  - number and the size of the batch.
  + logs: Dict, contains the return value of `model.train_step`. Typically,
  + the values of the `Model`'s metrics are returned. Example:
  + `{'loss': 0.2, 'accuracy': 0.7}`.
  """
  # For backwards compatibility.
  self.on_batch_begin(batch, logs=logs)
  @@ -697,8 +698,9 @@ class Callback(object):
  Arguments:
  batch: Integer, index of batch within the current epoch.
  - logs: Dict. Has keys `batch` and `size` representing the current batch
  - number and the size of the batch.
  + logs: Dict, contains the return value of `model.test_step`. Typically,
  + the values of the `Model`'s metrics are returned. Example:
  + `{'loss': 0.2, 'accuracy': 0.7}`.
  """
  @doc_controls.for_subclass_implementers
  @@ -725,8 +727,9 @@ class Callback(object):
  Arguments:
  batch: Integer, index of batch within the current epoch.
  - logs: Dict. Has keys `batch` and `size` representing the current batch
  - number and the size of the batch.
  + logs: Dict, contains the return value of `model.predict_step`,
  + it typically returns a dict with a key 'outputs' containing
  + the model's outputs.
  """
  @doc_controls.for_subclass_implementers
  