Step 2: Handle the constructor's error case

An error occurs when a negative size is passed to the constructor. At the top of exceptions.cpp, write a InvalidSize class to represent this error. This exception should take a string in its constructor and have a GetMessage() accessor that returns the string. Modify the construtor so that it throws this exception with an error message passed to the exception's constructor rather than printing an error message and calling exit(1). Write the code in main() to catch the exception and use cerr to print out the message returned by GetMessage().