PEP-517

[ZipFile]

By extent also PEP 518 and PEP 621.

This PR converts legacy setup.py build into PEP-517-compliant one.

Reason:

• pip since v25 (next major release) will drop support for editable builds for non-PEP-517 projects.
• This change makes it possible to remove generated code from the source tree (still present in source distribution, though), which lines up with latest Cython guidelines.

Questions:

1. Unfortunately it is not possible yet to replace python setup.py build_ext --inplace since there is no equivalent functionality within python -m build. But, do we really need to do it? pip install -ve . will build extension modules either way.
2. With this kind of build flow, moving away html code annotations is no longer needed, since they are not included by default in the sdist or wheel. Should we remove this step and just add htmls to gitignore?

[coveralls]

coverage: 94.246%. remained the same
when pulling adf46bb on ZipFile:pep-517
into abf2a25 on ets-labs:master.