updated for XCode 6 - switched from NSUInteger to unsigned long parameters in NSString stringWithFormat calls

[AndrewSB]

XCode 6 gives these as warnings, just updating the lib.

[AndrewSB]

Hey @pieceofsummer, was wondering whether you'd been able to take a look at this yet. I wanted to stop maintaining my fork, and I think this would make other people's lives easier too!