*   Adds option for introducing slack in the pipeline to reduce CPU
        contention, via `tf.data.Options().experimental_slack = True`
    *   Added experimental support for parallel batching to `batch()` and
        `padded_batch()`. This functionality can be enabled through
        `tf.data.Options()`.
    *   Support cancellation of long-running `reduce`.
    *   Now we use `dataset` node name as prefix instead of the op name, to