Support cookie and header paramers

[bessgeor]

OpenAPI spec allows specifying in: cookie and in: header for parameters. The problem is - there is no built-in facility in giraffe to bind cookies or headers (or at least I haven't found one), so it seems like we should either restrict those parameters to string type without a format or code-gen manual binding code. I believe that the solution must be common to both cookie and header, that's why I include them both into this issue.