Use semantic versioning for release tags

[brawer]

Could pyclipper tag its future releases according to semantic versioning? For example, the last release was tagged as 1.1.0.post3 which isn’t quite according to the spec; see test page. It’s certainly not the end of the world to ignore semver.org, but some Linux distributions actually assume that projects follow semantic versioning. Maybe pyclipper could simply tag its future releases as major.minor.patch?

[anthrotype]

Hi Sascha! I try to follow semver already. Those post-releases you see do not actually change the code of the library so downstream maintainers can ignore them, only CI metadata required to compile the wheel packages changes but that's only used by our own Travis or Appveyor setup. Sometimes I need to increment the version string because PyPI index doesn't accept the same package version uploaded more than once. The .post suffix are legal according to the python version specification PEP440

[anthrotype]

Sure, I could alternatively bump the third last digit (bugfix) every time, even when no actual code changes occur, but that would signal that something has changed where it has not, in practice.

[Cogitri]

It'd be nice if this was more prominently said in the README or so, since at least I didn't know what that post version was for until now.