Stores limit time/object pairs, keeping only the largest limit items.

Sample usage:

  l = SlowestTimes.new 5

  l << [Time.now, 'one']
  l << [Time.now, 'two']
  l << [Time.now, 'three']
  l << [Time.now, 'four']
  l << [Time.now, 'five']
  l << [Time.now, 'six']

  p l.map { |i| i.last }