GAZ hasDbXref to ISO_3166 countries

[ddooley]

GAZ offers up these database cross references for, e.g. Belgium

"hasDbXref": [
"ISO3166-1:BE",
"ISO3166-2:BE",
"ISO3166-1:BEL",
"ISO3166-1:056"
]
But there are actually sub-categories of ISO3166-1, and that's why what looks like a 1-many mapping is actually 1-1 if subcategory is taken into account. I'm not sure how exactly to represent it but something like?

hasDbXref 
  https://www.iso.org/obp/ui/#iso:code:3166:BE
  ISO_3166-1_alpha-2:BE
  ISO_3166-1_alpha-3:BEL
  ISO_3166-1_numeric:056
  ISO_3166-2:BE

More info at:
https://en.wikipedia.org/wiki/ISO_3166

Some related work: https://arxiv.org/pdf/0801.3908.pdf
https://www.slideshare.net/nichtich/encoding-changing-country-codes-in-rdf-with-iso-3166-and-skos