Upgraded code to build against `pipes-4.0.0`

I was going through reverse dependencies of `pipes` to upgrade downstream libraries that used the `pipes-3.0` API.  This pull request upgrades `pianola` to build against `pipes-4.0`.

Note that `pipes-4.0` eliminated the need for the proxy transformer system so there is no longer a `p` type parameter.  That means you probably don't need to use the `Produ` and `Consu` type synonymes any longer because now you can just use `Producer` and `Consumer` directly.  However, I'll leave that up to you to decide if you want to change that or not.