`FlushCaches()`.
    *   Add `auto_correlation` to distributions.
    *   Add `tf.contrib.distributions.Autoregressive`.
    *   Add SeparableConv1D layer.
    *   Add convolutional Flipout layers.
    *   When both inputs of `tf.matmul` are bfloat16, it returns bfloat16,
        instead of float32.
    *   Added `tf.contrib.image.connected_components`.