input: Write a function to find the top 5 most common characters in a string using the Counter class from the collections module.
  assert top_characters("This is a test sentence to use for the example.")==[('e', 5), ('s', 4), ('t', 4), ('o', 3), ('i', 3)]
  assert top_characters("Another example sentence.")==[('e', 4), ('n', 3), ('t', 2), ('A', 1), ('o', 1)]
  assert top_characters("A quick brown fox jumps over the lazy dog.")==[('o', 4), (' ', 7), ('u', 2), ('i', 1), ('c', 1)]
output: def top_characters(s):
      from collections import Counter
      count = Counter(s)
      return count.most_common(5)