Revert "Revert "fix version identifier to comply with PEP 440""

This reverts commit bdfb7095fa9d9d92b657a66444ee704e3ecf027e.
Revert "Revert "change PEP-440 version identifier to one that's actually accepted by pip/setuptools""

This reverts commit 4004ba6479b37596b3ac6ea2559ece117544a7c0.