Any chance of GRU/LSTM layers ?

[clive-g-brown]

Code Sample, a copy-pastable example if possible

# Your code here

Problem description

[this should explain why the current behaviour is a problem and why the expected output is a better solution.]

[christopherzimmerman]

I'd love to add these in. Primary issue is figuring out how to back propagate along layers that need more than one gradient. This will probably require more Num::Grad work than it will Num::NN work.