add lazy iterators

[jdonaldson]

Here's something else that I think will be useful. It's a bit different from your other "Lazy" class in that it only deals with iterators. But, the theme is the same.

[jdonaldson]

One other option is to have all these methods defined statically. You could get the same flow here with "using".

[kevinresol]

Reminds me of this again haxetink/tink_pure#1

[jdonaldson]

Yeah, that looks like the same idea, I figured you guys had something like this.

One small note, I see that you're using Sequence as an iterable. Wouldn't it be better to handle lazy operations solely within iterators? It would give more flexibility (e.g. it would work on iterators that cannot be repeated). A more specialized Sequence type could be built on top of it.

[back2dos]

Closing in favor of the other PR. This lib is getting big enough already ^^