'cell_clip' and 'proj_clip' for Flux: LSTM

Looking through the docs. , I found that this feature is missing for LSTM layers. It comes as an optional parameter in tensorflow LSTMCell This will be useful for porting stuff to flux while achieving the same results as from tensorflow implementations for some popular algorithms (like ELMo). Looking in the code base of tensorflow if says that it clip the value of cell states between [-cell_clip, cell_clip] in it's clip_by_value method.