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