Fix tuple_windows as lazy

[aobatact]

Fix #601 anyway because this change will reduce one clone.

[jswrenn]

I've rebased and rustfmt'd this PR, but it's still failing a test. Can you fix the bug?

[Philippe-Cholet]

I deleted my previous comment, it was wrong (I must have been sleeping ^^). We would definitely need to update size_hint but there is no issue about ExactSizeIterator (the resulting iterator being shorter than the inner one, not longer 😪). Probably

use crate::size_hint::{self, SizeHint};

// then
    fn size_hint(&self) -> SizeHint {
        size_hint::sub_scalar(self.iter.size_hint(), T::num_items() - 1)
    }

EDIT: I was partially wrong, but real fix committed.

[Philippe-Cholet]

@jswrenn This is ready for me, what do you think?