Modernize repo and make sure it works with ST4

[Frizlab]

That being said:

• I have no idea if it works before ST4 now;
• I have not succeeded in running the tests (UnitTesting shows a panel at the bottom, but it is desperately empty; I suspect a syntax error, or something of that nature, but I don’t know for sure and am not sure how to debug…);
• I have removed the support for vim modelines. There is a dedicated plugin for that if needed; let’s not mix everything up!
• I migrated the EoL from dos to unix;
• I removed things that I thought were useless; I hope they actually were!

[michaelblyons]

If you want to check ST3 compat, UnitTesting has a GH Action that can do it for you. There's probably not any divergence between platforms, so ST3, ST4 on Ubuntu is probably enough.

If you have CI minutes to burn. 😅

[Frizlab]

Yes I noticed the UnitTesting repo has a GitHub Actions for testing in the CI and thought about setting that up.

Thanks for the review! I have not finalized everything yet, the PR is still a draft for now (I have to implement the format change, cleanup the tests even more, etc.) I will do the changes you proposed/requested before marking the PR ready.