Pathlib2 switched to new syntax in setup.py without bumping major or minor version

[zvezdan]

The switch to new syntax for conditional dependencies in pathlib2-2.3.2 causes issues to automated build tooling that uses pex. This line: https://github.com/mcmtroffaes/pathlib2/blob/develop/setup.py#L47 used to be done in extras_require instead of install_requires.

Recent versions of setuptools and wheel are able to parse this new syntax, but older versions enforced by pex are not: https://github.com/pantsbuild/pex/blob/v1.4.5/pex/version.py#L9
Until recently, wheel was also forced to version that is not able to parse new syntax: https://github.com/pantsbuild/pex/blob/v1.4.4/pex/version.py#L11

This would be less of an issue if pathlib2 bumped a version in major or minor instead of just patch part of the version number. This is a breaking change for build systems that worked just fine with pathlib2-2.3.0.

I'm asking if we can do one or both of the following to fix this issue.

1. Revert to extras_require in version 2.3.x of pathlib, preferably 2.x and perhaps use it only for the next major version?
2. Perhaps avoid using the new syntax entirely? This is a backport package and those who need a backport package most probably do not have up-to-date environment anyway to parse the new features.

[mcmtroffaes]

Thanks for reporting and sorry for the delay in the response here. I've just pushed a release that uses the old deprecated syntax.