Project is stale

Today I needed `pathlib.Path.with_stem()`, which was introduced in Python 3.9 but my projects still support Python 3.8. I saw that this project advertised compatibility with future Python versions, so I was hopeful it would fix the issue, but it doesn't:

```
~ @ pip-run pathlib2
Python 3.12.1 (main, Dec 7 2023, 20:45:44) [Clang 15.0.0 (clang-1500.1.0.2.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pathlib2
>>> pathlib2.Path('foo/bar.baz').with_stem('bing')
Traceback (most recent call last):
File "", line 1, in
AttributeError: 'PosixPath' object has no attribute 'with_stem'
```

I can see that `with_stem` exists in the code base, but there just haven't been any releases since.

I see in #70 that the project was on the verge of cutting a release. Are there still plans to cut a release of the committed code? If not, maybe consider updating the readme to indicate the status.