WIP - Number to words localisation improvements

[hazzik]

I'm trying to improve experience and encourage users to localise ToWords/ToOrdinalWords extension methods.

I've introduced INumberToWordsConverter:

public interface INumberToWordsConverter
{
    string Convert(int number);
    string ConvertToOrdinal(int number);
}

Also I want to clarify how shall behave untranslated converter? Shall it throw NotSupportedException or just return number.ToString()?

[hazzik]

Related to #132

[thunsaker]

RE: Unsupported languages - Throwing an error would just upset people using it, at least the number would still have usable code.

[hazzik]

Yep, I do not like exceptions here as well

[MehdiK]

Awesome. I think we'll need to structure the Localisation folder a bit better; but good for now.

[MehdiK]

Thanks for the great work @hazzik. I think #132 should be fixed now! It's a shame we didn't have some failing tests for it; although admittedly we never tackled it directly.

[MehdiK]

Thanks for your great contribution @hazzik. This is now released to NuGet as v1.19.1.