fixed menubar width issue

the width of menubar is not changed when its parent window is resized

include/nana/gui/widgets/menubar.hpp

@@ -102,12 +102,15 @@ namespace nana
 		:	public widget_object<category::widget_tag, drawerbase::menubar::trigger>
 	{
 	public:
-		menubar();								///< The default constructor delay creation.
+		menubar() = default;					///< The default constructor delay creation.
 		menubar(window);						///< Create a menubar at the top of the specified window.
+		~menubar();
 		void create(window);					///< Create a menubar at the top of the specified window.
 		menu& push_back(const nana::string&);	///< Appends a new (empty) menu.
 		menu& at(size_t index) const;		    ///< Gets the menu specified by index.
 		std::size_t length() const;		        ///< Number of menus.
+	private:
+		::nana::event_handle evt_resized_{nullptr};
 	};//end class menubar
 }//end namespace nana
 #endif

source/gui/widgets/menubar.cpp

@@ -574,17 +574,27 @@ namespace nana
 
 
 	//class menubar
-		menubar::menubar(){}
 		menubar::menubar(window wd)
 		{
 			create(wd);
 		}
 
+		menubar::~menubar()
+		{
+			API::umake_event(evt_resized_);
+		}
+
 		void menubar::create(window wd)
 		{
 			widget_object<category::widget_tag, drawerbase::menubar::trigger>
 				::create(wd, rectangle(nana::size(API::window_size(wd).width, 28)));
 			API::attach_menubar(handle());
+			evt_resized_ = API::events(wd).resized([this](const ::nana::arg_resized& arg)
+			{
+				auto sz = this->size();
+				sz.width = arg.width;
+				this->size(sz);
+			});
 		}
 
 		menu& menubar::push_back(const nana::string& text)