Base Backup Engine types should extend this class and call parent::__construct in there constructor. Defines base functionality shared across all types of backups
 /**
  * Set the default backup filename.
  */
 public function __construct()
 {
     parent::__construct();
     $this->set_backup_filename(implode('-', array(str_ireplace(array('http://', 'https://', 'www'), '', home_url()), 'backup', current_time('Y-m-d-H-i-s'))) . '.zip');
     $this->excludes = new Excludes();
 }