Update rnn.py
Update rnn.py

Add capability for  LSTN layer:
1) getting a complete state RNN (c, h) from the stack as input instead to use a zero initialization . Use initial_state=True parameter for that. Default False.
2) putting a complete state RNN (c, h) in the stack as output instead to discard it. Use return_state=True parameter for that . Default False.
google/trax,google/trax