Created an ml directory for the ML stuff.
	modified:   Makefile
	modified:   ltr_algorithm.hpp
	modified:   ltr_main.cpp
	renamed:    linear_regression.cpp -> ml/linear_regression.cpp
	renamed:    linear_regression.h -> ml/linear_regression.h
	renamed:    ml_model.cpp -> ml/ml_model.cpp
	renamed:    ml_model.h -> ml/ml_model.h