An Iterator From Scratch

Implement EvensUpTo(int n): yields every even number from 0 to n inclusive, using yield return. n < 0 yields nothing. Also implement TakeEvens: returns the first count evens of a sequence (fewer if the source runs out). ``csharp static IEnumerable<int> EvensUpTo(int n); static IEnumerable<int> TakeEvens(IEnumerable<int> source, int count); ``