forward compatible code: by explicitly importing either
    `tensorflow.compat.v1` or `tensorflow.compat.v2`, you can ensure that your
    code works without modifications against an installation of 1.15 or 2.0.
*   EagerTensor now supports numpy buffer interface for tensors.
*   Add toggles `tf.enable_control_flow_v2()` and `tf.disable_control_flow_v2()`