Non-pickle based serialization

[martintb]

We should be able to use the inspect module to get all of the arguments passed to a constructor. If we store this dictionary, we should be able to use this for both serialization/deserialization but also for recreating Pipeline incantations.

My thought is to place this in PipelineOp and have the storage be automatic and opaque to the user.

The only weak point in this scheme is that, if the user dynamically changes any variables, this won't be reflected in the serialized Pipeline. A workaround would be to modify the getattr so that it looks in the storage dictionary first before looking in the class members.