support Directory Reference

Files
file	defer.hpp [code]
file	exception.hpp [code]
file	is_integer.hpp [code]
file	make_unique.hpp [code]
file	observer_ptr.hpp [code]
file	optional.hpp [code]
file	release_deleter.hpp [code]
file	to_string.hpp [code]
file	tribool.hpp [code]
file	windows.hpp [code]