Allow option of permitting extra command line options that haven't been defined in Getopt

Created by: rightaway

If I parse command line options and one of the options haven't been defined in Getopt (by doing addOption), there's an error because of the undefined option. I'd like to use Getopt in some code where the expected command-line options are defined dynamically and not always known up front. It would be great to have an option that allows for extra options on the command-line that haven't been defined. Such an option could be passed in when instantiating the Getopt object.