This function is used to add an entity to a scene.
void dg_scene_add_ent(dg_scene_t *scene, dg_entity_t *entity);
dg_scene_add_ent(scene, dg_ent_player());
void dg_scene_add_ent(dg_scene_t *scene, dg_entity_t *entity)
{
if (!scene || !entity)
return;
dg_arr_add_begin(&(scene->entities), entity);
}