Not sure how safe it is to completely remove setup.cfg file. Things are confusing due to historical move from setup.py, to setup.py/setup.cfg combination, to pyproject.toml. Not sure there isn't still something dependent on setup.cfg metadata for some versions of Python when installing from pure source code (not a wheel), or even for cibuildwheel itself. This is all going to have be explored more throughly before make changes.

First step is to look at just tox and pytest configuration as first step.

Rather than merge this, have made changes against develop branch to achieve same aims, but so can do it in parts, properly test and resolve any issues.

As I mentioned would do above, have extracted out configs into tox.ini and pytest.ini as appropriate. Have also dropped running of coverage as that wasn't being used and was in an unknown working state. Also found some other problems with GitHub actions tox configuration which had to be fixed up.

The general project meta and build config is still in setup.cfg in develop branch this has to go somewhere still and can't just be removed as this patch was doing.

So this PR is being superseded, but will leave open for now as will record progress of changes here.

Everything now dealt with in develop branch. If need to test for some reason use 2.1.0dev1 from PyPi.

Sounds good. Thanks @GrahamDumpleton