Added optional Culture parameter to NumberToWords

I personally don't like creating new objects on each call. Humanizer is likely to be called very frequently and I don't like to create thousands of objects in the memory waiting. I understand these objects are cheap to create and keep around; but that doesn't justify creating many objects.

I am not following this closely and as usual don't have a VS handy; but do we really have to create a new object on each call to be able to use the provided context? I doesn't look like it.