def without_any(*features)
      features = setify(*features)
      self.class.new Hash[@sets.select {|key, val| key.intersection(features).empty?}]
    end
def without_any(*features)
      features = setify(*features)
      self.class.new Hash[@sets.select {|key, val| key.intersection(features).empty?}]
    end
Return an instance of Sounds whose sets exclude all of the given
 features.