Introduce coroutine support (util/coro.hpp)

Implement coroutine types `lazy` and `generator` in stx namespace.
Implement fs::list_dir_recursively.

Utilities/File.h

@@ -804,4 +804,6 @@ namespace fs
 	}
 
 	file make_gather(std::vector<file>);
+
+	stx::generator<dir_entry&> list_dir_recursively(std::string path);
 }