Move to `pyproject.toml` instead of `setup.py`

[espenhgn]

This is now the new standard: https://packaging.python.org/en/latest/specifications/declaring-project-metadata/#declaring-project-metadata

[torbjone]

It would be nice if we could release v0.2 relatively soon, is this something that we should look into first, or should we postpone this to a later release?

[espenhgn]

Let's postpone this until it's in place in LFPykit, LFPy, and MEAutility. I still didn't see any deprecation warnings or such even when installing LFPy fresh for instance:

% conda create -n "lfpytest" python=3 pip -y
% conda activate lfpytest
% pip install lfpy

So we can release the current version as 0.2 as is, I think.

[espenhgn]

Well, this didn't go well:
https://github.com/LFPy/LFPykernels/actions/runs/5054546283/jobs/9069593692?pr=73

I'll try and fix it later but will start with LFPykit. Or do you want to investigate?

[torbjone]

In this case, I wonder if the problem was simply that the version ended up as '0.2.', with the trailing '.', and apparently it is common to include a patch version even if it is '0'.