code: def histogram(ratings, min_rating=None, max_rating=None):
      
      ratings = [int(r) for r in ratings]
      if min_rating is None:
          min_rating = min(ratings)
      if max_rating is None:
          max_rating = max(ratings)
      num_ratings = int(max_rating - min_rating + 1)
      hist_ratings = [0 for x in range(num_ratings)]
      for r in ratings:
          hist_ratings[r - min_rating] += 1
      return hist_ratings
docs: Generates a frequency count of each rating on the scale
      ratings is a list of scores
      Returns a list of frequencies