code: def to_s
        days = weekdays.map { |day| day.to_s.capitalize }
        last_day = days.pop
  
        days.empty? ? last_day : days.join(", ") + ", and " + last_day
      end
docs: Returns comma separated and capitalized in Sun-Sat order
   e.g. 'Mon, Tue, Wed' or 'Sat' or 'Sun, Sat'