def generate_next(tau)
      p = []
      @players.each do |player|
        p << Player.new(@raters[player.obj].rate(tau), player.obj)
      end
      self.class.new(p)
    end
def generate_next(tau)
      p = []
      @players.each do |player|
        p << Player.new(@raters[player.obj].rate(tau), player.obj)
      end
      self.class.new(p)
    end
Generate a new {RatingPeriod} with a new list of updated {Player}

 @return [RatingPeriod]