Implement pagination helpers without streams

[coryan]

As shows by the LRO changes, we can unconditionally implement a stream-like struct without having to implement the future::Stream trait, and then implement the stream trait conditionally.

That seems more friendly: the easy to use API is always available, and if you want streams (with all the StreamExt goodies) you can turn that on.

[coryan]

Can we close this? If not, what remains?