title: Replace tab in NSString with \t
body: <p>I'm parsing json with SBJson.<br>
  I receive an error "-JSONValue failed. Error is: Unescaped control character [0x09]" when parsing my json string, it has unencoded tab. How to replace this tab in my json string to \t? If i remove tab manualy, everything is good. Or how to encode this tab properly?</p>