Added -[NSData stringWithUTF8Encoding].
Added +[NSDate dateWithHTTPDateString:].
Added +[NSString stringWithUUID].
Added -[NSString stringWithURLPercentEncoding].
Added -[NSURL URLByAppendingQueryFromDictionary:].
Removed needless ampersand at the end of URLs returned by -[NSURL URLByAppendingQueryFromDictionary:].
Added umbrella header.