public static function addFileExtensions(array $extensions)
    {
        // get list of currently configured autoload-file-extensions
        $splExtensions = explode(',', spl_autoload_extensions());

        // merge existing extension and new extension and remove duplicates
        $splExtensions = array_unique(array_merge($splExtensions, $extensions));

        // set file extensions for spl
        spl_autoload_extensions(implode(',', $splExtensions));
    }