Sopel-amputator

* Added Twitter/X domains to default ignore list

Under-the-hood improvements:

* More robust domain matching against ignore list
* Includes distinct log messages for exact matches vs. subdomain matches
* More granular error handling
* Better error logging
* Migrated package metadata from `setup.py`+`setup.cfg` to `pyproject.toml`

Initial release.

Pending conversion from `setup.py`+`setup.cfg` template to newer style package
using `pyproject.toml`—plus some other features on the todo list—but the basics
are here:

* Detect likely AMP links
* Call AmputatorBot API for the canonical URL of each suspected AMP link
* Skip links from a configurable list of ignored domains
* Silently fail if no better URL is found