Fix: Fixing test for Checksum() method.
Fix: Marking test as slow.
Fix: Fixing Chunk() method.
Adding graph extension. graph.IsCyclic().
Adding IEnumerable extensions. Top(n), Bottom(n).
Fix: Fixing TimeSpan.Round().
Adding IEnumerable extension. HasCountOfAtLeast<T>(int count).
Adding IEnumerable extensions. Permutation<T>(r), Combination<T>(r).