trim -- 去除前後多餘空白
語法：string trim (string $str [, string $charlist ])
去除字串開頭和結尾的字元，回傳去除後的字串。如果第二個參數沒給值，預設會去除下列這些字元：
" " (ASCII 32 (0x20)), an ordinary space.
"\t" (ASCII 9 (0x09)), a tab.
"\n" (ASCII 10 (0x0A)), a new line (line feed).
"\r" (ASCII 13 (0x0D)), a carriage return.
"\0" (ASCII 0 (0x00)), the NUL-byte.
"\x0B" (ASCII 11 (0x0B)), a vertical tab.
如果要去除其它字元，可以在第二個參數裡設定。
去除字串開頭和結尾的字元，回傳去除後的字串。如果第二個參數沒給值，預設會去除下列這些字元：
" " (ASCII 32 (0x20)), an ordinary space.
"\t" (ASCII 9 (0x09)), a tab.
"\n" (ASCII 10 (0x0A)), a new line (line feed).
"\r" (ASCII 13 (0x0D)), a carriage return.
"\0" (ASCII 0 (0x00)), the NUL-byte.
"\x0B" (ASCII 11 (0x0B)), a vertical tab.
如果要去除其它字元，可以在第二個參數裡設定。