Static country codes

[filippomenchini]

It would be nice to have static country codes.
Example:

class CountryCodes {
    static String Italy => "IT";
    static String Usa => "US";
    // and following...
}

Then, you would use them like this:

final artist = tidal.artist.getSingleArtist(id: 1234, countryCode: CountryCodes.Italy);