packaging: refactor and drop pbr
Drop problematic pbr in favor of recommended modern python packaging setup:
https://packaging.python.org/tutorials/packaging-projects/
Versioning is now handled by miniver without introducing external dep:
https://github.com/jbweston/miniver
I've also updated and extended setup.cfg with more metadata for better integration on PyPI and elsewhere.
Fixes: #41 (closed)