title: Listing all country codes of phone numbers
body: <p>I'd like to have the country code list for phone numbers. Such as, United State (+1), United Kingdom (+44) ... I know that libphonenumber is a great tool to help phone parsing, formatting and validation. However, it doesn't seem to have the functionality for listing all country codes. But those data should be within the metadata in libphonenumber, right? Does anyone have experience on this? </p>