Attempts to create the directory specified by
pathname.
Note that you probably want to specify the mode as an
octal number, which means it should have a leading zero. The
mode is also modified by the current umask, which you can
change using umask().
注: Mode is ignored on Windows, and became optional in PHP 4.2.0.
The mode is 0777 by default, which means the widest
possible access. For more information on modes, read the
details on the chmod() page.
成功回傳TRUE失敗回傳FALSE。
See also rmdir().