Implement validation() method for SceneTexture.
diff --git a/src/scene.h b/src/scene.h
index 9638653..a6f5c46 100644
--- a/src/scene.h
+++ b/src/scene.h
@@ -142,6 +142,7 @@
     void teardown();
     void update();
     void draw();
+    ValidationResult validate();
 
     ~SceneTexture();