versioneer may be no longer actively developed [1].

setuptools_scm seems to be a viable less complex alternative. A
disadvantage of setuptools_scm
is that it doesn't return the version appropriate to the current git
repository state but the version of the repository from the last
invocation of setup.py.

setuptools_scm uses the .devN suffix correctly [2] in that X.Y.devN
signifies the development of the not yet released X.Y! Versioneer
assumend X.Y to be the last release. To avoid confusion here we use the
form with an additional .post1 suffix so that the next version number
needn't be guessed.

These changes also require adaptions in doc/conf.py where the revision
id of the release is used to link to the code on GitLab!

[1] https://github.com/pydata/xarray/issues/2853
[2] https://www.python.org/dev/peps/pep-0440/