Given a string, create a function to reverse the case. All lower-cased letters should be upper-cased, and vice versa.
ReverseCase("Happy Birthday") ➞ "hAPPY bIRTHDAY"
ReverseCase("MANY THANKS") ➞ "many thanks"
ReverseCase("sPoNtAnEoUs") ➞ "SpOnTaNeOuS"N/A