will now build a 5-layer LSTM stack where each layer shares the **same**
    parameters. To get 5 layers each with their own parameters, write:
    `MultiRNNCell([LSTMCell(...) for _ in range(5)])`. If at all unsure, first
    test your code with TF 1.1; ensure it raises no errors, and then upgrade to
    TF 1.2.
*   RNNCells' variable names have been renamed for consistency with Keras