Added failing test for three digit number validating with card type amex and some other tests for validating CVC that are good to have
Removes 3..4 digit range for amex cvc security codes
Ran cake build
Change README to reflect 3- or 4-digit decision with AMEX and change tests
Merge pull request #40 from kulte/correct_amex_cvc_validation

Correct amex cvc validation