Support for multiple types in the model inputs

[eublefar]

I have wrapped ndarray::Array into an enum InputTensor with variants containing specific ndarray element types. I have modified Session to use this InputTensor enum along with match expression to destructure enum into ndarray::Array.

This change is not backward compatible. Probably could be implemented in backward compatible way with some trait bounding magic or additional run method but I am not sure what could be the best way to do it.