method for applying custom transformation functions.
    *   Several custom transformation functions have been added, including
        `tf.contrib.data.batch_and_drop_remainder()` and
        `tf.contrib.data.sloppy_interleave()`.
*   Add `train_and_evaluate` for simple distributed `Estimator` training.
*   Add `tf.spectral.dct` for computing the DCT-II.
*   Add Mel-Frequency Cepstral Coefficient support to `tf.contrib.signal` (with