Modernise build proccess

Since last release a lot has changed in python packaging world, setup.py is pretty much legacy now.

Notes:

• Looks like project on Travis is no more. Should we rewrite it to GH Actions?
• Should we bump minimal Python version to 3.8? Previous are EOL-ed.

I've a few more changes planned for release workflow. I'll see if I would be able to carve out some time in the coming week.

Thanks for the PR :) I'll try to bring over your changes into what i'm thinking.