`tf.train.experimental.enable_mixed_precision_graph_rewrite()`.
*   Add environment variable `TF_CUDNN_DETERMINISTIC`. Setting to "true" or "1"
    forces the selection of deterministic cuDNN convolution and max-pooling
    algorithms. When this is enabled, the algorithm selection procedure itself
    is also deterministic.

## Breaking Changes

*   Many backwards incompatible API changes have been made to clean up the APIs