asyncstream: Some of the example code was wrong
asyncstream: Some of the example code was wrong

Problem

`*::` only works on `Future[Spool[A]]`, not `Spool[A]`, and
 `Spool.LazyCons` is private, so that's not good too.

Solution

Wrap Spools in `Future.value` to get the API to work, and use `*::`
directly instead of using `Spool.LazyCons`.

finagle/finagle.github.io,finagle/finagle.github.io,finagle/finagle.github.io