-registering same system multiple times only replace pointer for callback

-added export attributes (required by windows to make DLL library, not work at now due to DMD bugs)
-interface D files to import

source/ecs/id_manager.d

@@ -33,7 +33,7 @@ struct IDManager
         m_ids_array[entity.id.id].entity = &entity;
     }
 
-    Entity* getEntityPointer(EntityID id)
+    export Entity* getEntityPointer(EntityID id)
     {
         Data* data = &m_ids_array[id.id];
         if (data.counter != id.counter)
@@ -42,7 +42,7 @@ struct IDManager
             return data.entity;
     }
 
-    bool isExist(EntityID id)
+    export bool isExist(EntityID id)
     {
         Data* data = &m_ids_array[id.id];
         return data.counter == id.counter;