Version '0+unknown'

[cbouy]

With the current installation process, when running prolif.__version__ in a python script, it will return "0+unknown" if users have installed a non-tagged version with the command pip install git+https://github.com/chemosim-lab/ProLIF.git.

The only way to get a proper version string is to either:

• Install from a tagged release: pip install https://github.com/chemosim-lab/ProLIF/archive/v0.3.0.zip
• Clone this repository and run pip install . or pip install -e .

Since this will happen mostly because ProLIF is not available on PyPI yet (see #6), and there's a workaround to get the version (pip list | grep prolif), I won't fix it.