getByCode for United Kingdom

[freyjajokulsd]

Currently the United Kingdom is one of the countries that does not have an alpha3
See: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#Exceptional_reservations'

It could be useful to have the getByCode method return the Great Britain country code for UK so that is has an alpha3 and so that the following statement is true:

United Kingdom is officially assigned the alpha-2 code GB

For an example CountryCode.getByCode("UK") would return CountryCode.GB and therefore .alpha3 will not throw a NPE like it does for CountryCode.UK