util/countries.go
func IsISOCountryCode(in string) bool {
	in = strings.ToUpper(in)
	_, ok := countries[in]
	return ok
}
func IsISOCountryCode(in string) bool {
	in = strings.ToUpper(in)
	_, ok := countries[in]
	return ok
}
// IsISOCountryCode returns true if the input is a known two-letter country
// code.
//
// TODO: Document where the list of known countries came from.