Append4 final

@pchiusano @fthomas @radekm 

I have created the pull request and as we expected is quite a massive one :-(

Anyhow on wiki are the release notes which I think has to be updated, I just wrote some of the stuff in. 
Lets review this and when we will be ok with whats in we just can do final formating and merge. 

Also notably, the tests are passing :-)

P.

Would it be ok if I rename this to `zipWithPrevious` because we already have the similar `zipWithIndex` and `zipWithState` processes? I would also add an `this |>` alias to `Process1Ops`