clone() added to MlModel, Activation and LearningRate.
	modified:   ml/learning_rate.cpp
	modified:   ml/learning_rate.h
	modified:   ml/linear_regression.cpp
	modified:   ml/linear_regression.h
	modified:   ml/ml_model.cpp
	modified:   ml/ml_model.h
	modified:   ml/neural_net.cpp
	modified:   ml/neural_net.h
	modified:   ml/neural_net_activation.cpp
	modified:   ml/neural_net_activation.h