This commit makes the build of Python packages use `setuptools` instead
of the deprecated `distutils` in `setup.py` files. See
[PEP 632](https://peps.python.org/pep-0632/) for more information on the
deprecation of `distutils`.

Note that using `setuptools` instead of `distutils` removes the
following user warning messages when creating the `bdist` and `sdist` of
the consumer and producer projects:

```
/usr/lib/python3.8/distutils/dist.py:274: UserWarning: Unknown distribution option: 'setup_requires'
  warnings.warn(msg)
/usr/lib/python3.8/distutils/dist.py:274: UserWarning: Unknown distribution option: 'install_requires'
  warnings.warn(msg)
```

This includes read-only buffers.

The code split between bytes and numpy array is removed and all objects
are now handled equally.

Furthermore, it seems to be more correct to increase the ref count for
None objects as well, while a pointer to that object is used.

This adjusts the paths of the pkg-config files so that they match
the installation locations of the actual libraries (always in
prefix/lib, not prefix/lib64).  It also fixes the paths within the
pkg-config files themselves, which were incorrect.