code: def fetch_exemplars(keyword, outfile, n=50):
      
      list_urls = fetch_lists(keyword, n)
      print('found %d lists for %s' % (len(list_urls), keyword))
      counts = Counter()
      for list_url in list_urls:
          counts.update(fetch_list_members(list_url))
      # Write to file.
      outf = io.open(outfile, 'wt')
      for handle in sorted(counts):
          outf.write('%s\t%d\n' % (handle, counts[handle]))
      outf.close()
      print('saved exemplars to', outfile)
docs: Fetch top lists matching this keyword, then return Twitter screen
      names along with the number of different lists on which each appers..