(PHP 5 >= 5.3.0, PHP 7)
遍历一个文件系统行为类似于 glob().
$pattern
   [, int $flags = FilesystemIterator::KEY_AS_PATHNAME | FilesystemIterator::CURRENT_AS_FILEINFO
  ] )$path
   [, int $flags = FilesystemIterator::KEY_AS_PATHNAME | FilesystemIterator::CURRENT_AS_FILEINFO | FilesystemIterator::SKIP_DOTS
  ] )