*   `tf.estimator`:
    *   `Estimator`s now use custom savers included in `EstimatorSpec` scaffolds
        for saving SavedModels during export.
    *   `EstimatorSpec` will now add a default prediction output for export if
        no `export_output` is provided, eliminating the need to explicitly
        include a `PredictOutput` object in the `model_fn` for simple use-cases.