unpipe?

Is there a way to [`unpipe`](http://nodejs.org/api/stream.html#stream_readable_unpipe_destination) individual consuming streams from Highland sources? (I.e. the opposite of `pipe()`.) I've resorted to using `destroy()` in its absence, but that's more the nuclear option.

Start with the Node.js Readable.unpipe documentation linked in the issue, then inspect Highland's existing pipe and destroy behavior. Determine how an individual consuming stream could be detached without destroying the source, and verify that other consumers continue working. The issue names no source files or tests, so the relevant implementation and validation points must be located first.

Written by the indexing model from the issue text.