A few things

Make child entites work.

z-sort entity list before rendering.

entites have a creation timestamp.

include/Engine/Entity/Hud.h

@@ -7,5 +7,5 @@ namespace Engine {
 
 class Engine::Hud : public Engine::Renderable {
 public:
-    Hud() : Renderable({0, 0}, 0) {};
+    Hud() : Renderable({0, 0}, 0, 0) {};
 };