Add new NSJSONSerialization extension.
API Change: NSFileManager+RFKit, fileSizeForPath: will return -1 if error occurs.
UIView+RFKit add animateWithDuration:delay:options:animated:beforeAnimations:animations:.
Document improve.
NSNumberFormatter+RFKit add formatedFileSizeStringWithBytes:useBinaryUnites:.
Fix warning: dout, no previous prototype for function.