Umlauts not supported

[gucki]

Is:

%w(Birnen Äpfel Zitronen).natural_sort
=> ["Birnen", "Zitronen", "Äpfel"]

Correct would be:

%w(Birnen Äpfel Zitronen).natural_sort
=> ["Äpfel", "Birnen", "Zitronen"]

[johnnyshields]

I imagine this affects any type of accent. I'd accept a PR for this if it is generic.

[MGPalmer]

This works if you have ActiveSupport:

%w(Birnen Äpfel Zitronen).sort do |a, b|
      NaturalSort.comparator(
        ActiveSupport::Inflector.transliterate(a),
        ActiveSupport::Inflector.transliterate(b)
      )
end