#179 Make OpenStemmata a Python package

[clemsciences]

The main benefit of the suggested changes is to simply do pip install -e . at the root of the project to install the openstemmata project. The best would be to host the code on Pypi so that a simple pip install openstemmata will install the project.
I also made code more Pythonic. I know this is a matter of taste.
The main drawback is that I moved all the data files into src/openstemmata. This change may break all previous scripts based on this project.

The next task will be to add a built-in reader in the package (see #178).

[Jean-Baptiste-Camps]

Thanks a lot for this work ! As it is an important change, I think we need to discuss it between maintainers, and see how to accomodate with them.

[Jean-Baptiste-Camps]

I wonder if one option could not be to have a separate repo under OpenStemmata for the python package, and keep the 'working database' separate 🤔

[clemsciences]

I think it could be possible.