*   C API: Renamed `TF_Port` to `TF_Output`.
*   C API: The caller retains ownership of `TF_Tensor` objects provided to
    `TF_Run`, `TF_SessionRun`, `TF_SetAttrTensor` etc.
*   Renamed `tf.image.per_image_whitening()` to
    `tf.image.per_image_standardization()`
*   Move Summary protobuf constructors to `tf.summary` submodule.
*   Deprecate `histogram_summary`, `audio_summary`, `scalar_summary`,