XXA, XXB, XXC & XXX missing in CountryAlpha3

[mathijstemper]

We use your package for converting between codes, countries and names on Identity Documents. Currently we run into errors that the XXA, XXB, XXC & XXX are not in the CountryAlpha3 while, according to the ISO/IEC 7501-1 (extending the ISO 3166-1) they can be related to stateless, refugees or unspecified nationalities.

• XXA is used to represent a stateless person, as defined in Article 1 of the 1954 Convention Relating to the Status of Stateless Persons
• XXB is used to represent a refugee, as defined in Article 1 of the 1951 Convention Relating to the Status of Refugees as amended by the 1967 Protocol
• XXC is used to represent a refugee, other than as defined above
• XXX is used to represent a person of unspecified nationality

I think these can translate to the XX Alpha 2 code.

What do you think?