Support PyTorch Models

[cxhernandez]

I think this will become a very useful feature in the future.

[cxhernandez]

cc @rbharath @miaecle @lilleswing if y'all at deepchem are interested

[rbharath]

+1. Could be a useful feature for hyperparameter searching!

[cxhernandez]

Going to try an example with this library: https://github.com/dnouri/skorch