Add namespaces

	modified:   README.md
	modified:   main.cpp
	modified:   search_engine/includes/vsm_engine.h
	modified:   search_engine/vsm_engine.cpp
	modified:   utils/database.cpp
	modified:   utils/document.cpp
	modified:   utils/includes/database.h
	modified:   utils/includes/document.h
	modified:   utils/includes/inverted_index.h
	modified:   utils/includes/query.h
	modified:   utils/includes/result.h
	modified:   utils/includes/term.h
	modified:   utils/inverted_index.cpp
	modified:   utils/query.cpp
	modified:   utils/result.cpp
	modified:   utils/term.cpp