d375: tf.Transform preprocessing for Machine Learning

tf.Transform: https://research.googleblog.com/2017/02/preprocessing-for-machine-learning-with.html

tf.Transform allows users to define a preprocessing pipeline. Users can materialize the preprocessed data for use in TensorFlow training, and also export a tf.Transform graph that encodes the transformations as a TensorFlow graph. This transformation graph can then be incorporated into the model graph used for inference.