+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?
HOLD YOUR HORSES!

    case Ast.ZipWith(name, op) :: Ast.Map(op2) :: rest => Ast.ZipWith(name, op andThen op2) :: rest