CFG:U: Implemented the GetCountryCodeID and GetCountryCodeString

I couldn't find a way to retrieve all the country code strings, and the ones in there need to be checked, probably using a real 3DS.
Does the 3DS send those strings with a NULL terminator? that's another thing that has to be checked on a real 3DS.
Use `// TODO(Subv):` or '/// @todo:'''. The former is more consistent with other places in the code, the latter is doxygen format. I don't think the format you currently are using is valid for doxygen.