Add listbox::clear_headers() and menubar::clear()

Added listbox::clear_headers() to remove all the columns from the listbox
Added menubar::clear() to remove all the items from menubar

source/gui/widgets/listbox.cpp

@@ -307,6 +307,11 @@ namespace nana
                     return cont_.back().index;
 				}
 
+				void clear()
+				{
+					cont_.clear();
+				}
+
 				unsigned pixels() const noexcept  ///< the visible width of the whole header
 				{
 					unsigned pixels = 0;
@@ -5319,6 +5324,14 @@ namespace nana
 			return pos;
 		}
 
+		void listbox::clear_headers()
+		{
+			internal_scope_guard lock;
+			auto & ess = _m_ess();
+			ess.header.clear();
+			ess.update();
+		}
+
 		listbox::cat_proxy listbox::append(std::string s)
 		{
 			internal_scope_guard lock;

source/gui/widgets/menubar.cpp

@@ -625,6 +625,13 @@ namespace nana
 		{
 			return get_drawer_trigger().ess().items.size();
 		}
+		
+		void menubar::clear()
+		{
+			internal_scope_guard lock;
+			get_drawer_trigger().ess().items.clear();
+			API::refresh_window(handle());
+		}
 
 		bool menubar::cancel()
 		{