Adding a prefab for the load screen

prefabs/loading.gcprefab

@@ -0,0 +1,11 @@
+<gc_entities>
+    <gc_entity>
+        <transform_component>
+            <Size x="800" y="600" />
+        </transform_component>
+        <renderer src="loading">
+            <Rect height="auto" width="auto" top="0" left="0" />
+        </renderer>
+        <fixed_to_cam x="50%" y="50%" width="100%" height="100%" />
+    </gc_entity>
+</gc_entities>

prefabs/mainmenu.gcprefab

@@ -2,6 +2,7 @@
     <data>
         <sprite name="panel" src="assets/ui/panel.png" />
         <sprite name="button_background" src="assets/ui/button_background.png" />
+        <sprite name="loading" src="assets/ui/panel.png" />
         <font src="assets/fonts/roboto.ttf" />
     </data>
     <gc_entities>

src/main_menu.c

@@ -15,7 +15,11 @@
 bool start_button(gc_engine *engine, gc_entity *entity, gc_vector2 _, \
 enum gc_mousekeys __)
 {
-    gc_scene *scene = scene_create(engine, "prefabs/game.gcprefab");
+    gc_scene *scene;
+
+    prefab_load(engine, "prefabs/loading.gcprefab");
+    engine->game_loop(engine, 0);
+    scene = scene_create(engine, "prefabs/game.gcprefab");
     if (!scene) {
         engine->should_close = true;
         my_printf("The game scene couldn't be loaded.\n");