been moved back to the core namespace. This includes `RNNCell`, `LSTMCell`,
    `GRUCell`, and a number of other cells. These now reside in `tf.nn.rnn_cell`
    (with aliases in `tf.contrib.rnn` for backwards compatibility). The original
    `tf.nn.rnn` function is now `tf.nn.static_rnn`, and the bidirectional static
    and state saving static rnn functions are also now back in the `tf.nn`
    namespace.