Use ISO3166 country names

[petri]

This makes it easier to map the country-specific codes to country data in other systems. The names can be found for example in the python "iso3166" package.

[petri]

This was not included in 2.0 PR code. Reopening.

[petri]

The pycountry package might also be useful.

[psolin]

ISO-20275 uses 3166-1 country codes, so I think we will be covered.

[petri]

I just pushed a iso3166map branch with countries.csv semicolon-separated file that maps all terms_by_country country names to corresponding 2-letter iso3166 codes.