Add Support for `torch.nn.RNN` and `torch.nn.RNNCell` Modules

[coreylammie]

Support should be added for torch.nn.RNN and torch.nn.RNNCell modules.

[coreylammie]

This has been partially actioned in #134. I have implemented logic for the legacy routine (for both standard and bidirectional RNN modules with an arbitrary number of layers). Logic is still required for the crossbar mapping of different tensors and memristive inference routine, however.