Provide hook to handle status codes

[Altreus]

I couldn't figure out how to do this easily but I might put more effort into it if no one can see an obvious way of doing it quickly.

Basically, I would like to handle 4xx errors from webservices that have codes outside of the standard set: Twitter and Discord have different rate-limiting status codes (420 and 429 respectively), but I'm having trouble creating a role that correctly extends request.

It would be far easier if I could supply a method that was able to retry, but I don't know enough Perl6 yet to refactor request such that it can still .emit properly.

So I will be experimenting with my own patches for academic purposes but I beseech thee to write it properly for the good of the future :)