static function Instance()
 {
     if (null === MainWP_Wordpress_SEO::$instance) {
         MainWP_Wordpress_SEO::$instance = new MainWP_Wordpress_SEO();
     }
     return MainWP_Wordpress_SEO::$instance;
 }
 function wordpress_seo()
 {
     MainWP_Wordpress_SEO::Instance()->action();
 }