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.

well I think negative number does not make sense in take. I do not have strong preference on this if you like previous implementation feel free to revert it. I think we may go to `require` here for < 0, however in that case I would like to wrap take in go, so we won't re-assert ourselves on every. step. Maybe same treatment shall be applied to other combinator using `require` - the `window`...