v0.4.20231004: new release, mainly switch to pyproject.toml

What's Changed

• small ci updates; remove python2 compat stuff by @karlicoss in #64
• update to src/ structure and use pyproject.toml by @karlicoss in #65
• ci updates by @karlicoss in #66

Full Changelog: v0.3.2...v0.4.20231004