GDataDateTimeオブジェクトの作成
+ (GDataDateTime *)dateTimeWithDate:(NSDate *)date timeZone:(NSTimeZone *)tz { return [[[GDataDateTime alloc] initWithDate:date timeZone:tz] autorelease]; }
+ (GDataDateTime *)dateTimeWithDate:(NSDate *)date timeZone:(NSTimeZone *)tz { return [[[GDataDateTime alloc] initWithDate:date timeZone:tz] autorelease]; }