+str - adds ZipWith and makes Zip use that to create tuples/pairs

@patriknw @ktoso @2m @bantonsson, do we want this one? Or is Flexi replacing all the things?
There is no point in naming it, because it already has a name. If you want to give it another name, use ZipWith and specify your own name or omit a name. `Zip` is just a convenience over `ZipWith` for the extremely common use of producing tuples/pairs.