Started integrating the learning framework to the package. It compiles,
but not everything has been implemented yet (reset() and advance()).
	modified:   ltr_main.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