Improve developer experience

With this MR, the whole build process is based on Meson. It drops setup.py, so we no longer have to maintain two build systems.

The project is installed as a proper python library with the use of meson-python. It supports a meson-based workflow as well as a python-native workflow using a venv and pytest for testing.

1 new option has been added to the meson build:

• pkgconf - include the pkgconfig file in the installation. If installed from sdist or wheel, a pkgconfig file cannot be installed

• Build with Meson only
• Fix coverage numbers - files are counted twice
• Describe developer flow (pythonic/meson-based)
• Update documentation

---

See also:

• https://docs.scipy.org/doc/scipy/building/understanding_meson.html
• https://meson-python.readthedocs.io/en/latest/how-to-guides/editable-installs.html