lwtnn/lwtnn: Release for Athena v21

We've added lots of new features since release v1.0: New layers: we now support batch normalization, highway layers, and GRUs Regression tests with Travis CI Test scripts to compare Keras NNs evaluation with lwtnn Also quite a lot of refactoring: The classes have been split into "low-level" code in Stack and "high-level" interfaces in LightweightNeuralNetwork The recurrent classes have been merged into Stack and LightweightNeuralNetwor