add update

src/layer/layer.hpp

@@ -19,6 +19,7 @@ namespace VE
     public:
       virtual void on_attach() {};
       virtual void render() {};
+      virtual void update() {};
       virtual void on_event(event e) {};
 
     protected:

src/utils/define.hpp

@@ -7,6 +7,7 @@
   public:\
     void on_attach() override;\
     void render() override;\
+    void update() override;\
     void on_event(VE::event e) override
 
 #define VE_CONNECT(DEF_CLASS) VE::event_manager::instance().connect(std::bind(&DEF_CLASS::on_event, this, std::placeholders::_1));