Modernize packaging

[Exirel]

In preparation for Sopel 8 and with the ongoing effort to modernize packaging everywhere:

• Added a pyproject.toml for modern packaging
• Added a Makefile to perform make develop build ("release" could be added, if asked)
• Removed setuptools packaging information from setup.cfg
• Removed setup.py
• Moved code from __init__.py into plugin.py, as to prepare future change (with config and stuff)
• Added flake8, pylint, and pyroma linters
• Added a "if sopel 8" bit to properly manage IRC identifiers once Sopel 8 is out

To release on pypi, use python -m twine upload dist/* after using the make build command.

You can now use make develop to automatically update your virtualenv and have an editable install.

[dgw]

The Makefile and added dev-tools is a bit more than just "Modernize packaging", but I know you mean well 🤪

[dgw]

@Exirel If you can get back to this soon-ish, that'd be helpful. Otherwise I will most likely implement my own subset of it—just the packaging and "if Sopel 8" parts, no extra tooling—for a version-bump compatible with Sopel 8.0.

[Exirel]

@Exirel If you can get back to this soon-ish, that'd be helpful.

Yup, done!

Edit: I'm waiting on your approval to squash these commits.

[dgw]

Have I tested all the extra build/dev tools? No, lol. But I trust you to create a better dev environment than me, at this point.

About all I can say about this rework is that it's probably not necessary to keep the py2 stuff (e.g. encoding comment) around. sopel-slap 0.1 will work with Sopel 7.x indefinitely, and 0.2 could just be for 8+ only now that 8.0 has released.

[dgw]

While awaiting a squash, I have set up Trusted Publishing for this repository so I can easily cut a new release post-merge. 😺

[Exirel]

Github is annoying, it didn't send me the approval email notification, so I didn't see it until now. Will see if I can manage that tonight.

[Exirel]

Squashed and I removed 3.7 as well.

[dgw]

Little backward-compatibility nit, sorry 😅