Future of pipes

[hongaar]

Similar to #29, but for piping. This is actually a more common feature of Vorpal, and mentioned and demoed on the wiki/website. But like sessions, it does add quite a lot of noise to the source code currently, and I wonder how many use cases there actually are for this feature.

The obvious alternative for this feature is core shell piping functionality.

If we decide to keep it in the Vorpal code, it'd be a good candidate to be refactored.

[AdrieanKhisbe]

To me it doesn't really compare to sessions, as they dont need a extra package to work.
(so we can have no idea of how much this is used)

Beside, I can't even consider some cli interpreter like bash not having piping feature.

But sure, it won't suffer a (potentialy massive) refactor :)