improve the timer that it can be deleted in elapse handler

include/nana/gui/timer.hpp

@@ -48,7 +48,7 @@ namespace nana
 		template<typename Function>
 		void elapse(Function && fn)
 		{
-			elapse_.connect(std::forward<Function>(fn));
+			elapse_->connect(std::forward<Function>(fn));
 		}
 
 		void reset();
@@ -66,7 +66,7 @@ namespace nana
 	private:
 		unsigned _m_interval() const;
 	private:
-		nana::basic_event<arg_elapse> elapse_;
+		std::shared_ptr<nana::basic_event<arg_elapse>> elapse_;
 		implement * const impl_;
 	};
 }//end namespace nana