Implemented cuDNN softmax but it is not currently passing tests.

\__eq__ and \__hash__ are bad.  tensor_format and mode definitely affect the computation and it could be said that algo does too.

I would advise to replace those methods by `__props__ = ('tensor_format', 'mode', 'algo')` as per http://deeplearning.net/software/theano/extending/op.html#__props__.