eager vs lazy evaluation

[rapus95]

Maybe we could begin unifying the iterator interface to a lazy only version to get people used to materializing manually where needed. Then we should add some Cache iterator and a materializing function though. The latter one would probably just call collect. The Cache iterator would be needed to prevent the situation that originally made Base use eager evaluation as the default.

[oxinabox]

Closed by #103 and just generally julia moving on