def with(*features)
      pos, neg = mangle_args(*features)
      self.class.new(Hash[@sets.select do |key, val|
        !key.intersection(pos).empty?
      end]).without_any(neg)
    end
def with(*features)
      pos, neg = mangle_args(*features)
      self.class.new(Hash[@sets.select do |key, val|
        !key.intersection(pos).empty?
      end]).without_any(neg)
    end
Return an instance of Sounds whose sets include any of the given
 features.