Some version formats cannot be parsed

[Krystofee]

Problem

For example Black autoformatter version could not be parsed by pip-upgrader.

krystofrehacek@Krystof-MacBook-Pro:retino/src ‹1213-update-npm-and-pip*›$ pip-upgrade

Found valid requirements file(s):
requirements.txt
black==19.10b0 error while parsing version
2/47: coreapi ... up to date: 2.3.3
3/47: dicttoxml ... up to date: 1.7.4
4/47: Django ... upgrade available: 3.0.2 ==> 3.0.5 (uploaded on 2020-04-01 07:59:15)
... output continues ...

Proposed solution

Support for this kind of versioning (e. g. 19.10b0) should be added, since pip accepts it.

[jhermann]

PEP 440 -- Version Identification and Dependency Specification | Python.org is the relevant spec, BTW.