feat(lib/challenge): HTTP meta refresh challenge method (#623)

* feat(lib/challenge): HTTP meta refresh challenge method

Closes #95

This challenge method enables users that don't (or won't) support
JavaScript to pass Anubis challenges. It works by using HTML meta
refresh directives to ensure that the client is a browser.

This is OFF by default. In order to enable it, an administrator MUST
choose to make the default challenge method `metarefresh`.

TODO(Xe):

- [ ] Documentation on this challenge method
- [ ] Amend wording around Anubis being a proof of work proxy in the docs
- [ ] Add configuration file syntax for the default challenge method and settings
- [ ] Test with early customers

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: spelling

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib/challenge/metarefresh): use this value of err

Signed-off-by: Xe Iaso <me@xeiaso.net>

* docs: add metarefresh challenge info, Web AI Firewall Utility

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>

README.md

@@ -43,7 +43,7 @@ Anubis is brought to you by sponsors and donors like:
 
 ## Overview
 
-Anubis [weighs the soul of your connection](https://en.wikipedia.org/wiki/Weighing_of_souls) using a proof-of-work challenge in order to protect upstream resources from scraper bots.
+Anubis is a Web AI Firewall Utility that [weighs the soul of your connection](https://en.wikipedia.org/wiki/Weighing_of_souls) using one or more challenges in order to protect upstream resources from scraper bots.
 
 This program is designed to help protect the small internet from the endless storm of requests that flood in from AI companies. Anubis is as lightweight as possible to ensure that everyone can afford to protect the communities closest to them.