Implement bit iterator

[Veykril]

I think a bit iterator that returns true and false for each bit correspondingly would be a nice addition to this library. I was in need of one which is why I already personally implemented it, though I am not sure about its performance.

The use case I have for it for example, is that one could zip this iterator with an iterator over a Vec and filter out all elements where the corresponding bit is unset for example.

[bluss]

Sounds cool, but I think we will struggle to deliver good performance through Iterator::next (maybe fold will be fine). The filtering operation could maybe even have a more specialized api.