Update to pyproject.toml

[jcupitt]

Install on ubuntu currently produces this message:

$ pip install pyvips
Collecting pyvips
  Using cached pyvips-2.2.1.tar.gz (633 kB)
  Preparing metadata (setup.py) ... done
Requirement already satisfied: cffi>=1.0.0 in /home/john/vips/lib/python3.11/site-packages (from pyvips) (1.15.1)
Requirement already satisfied: pkgconfig in /home/john/vips/lib/python3.11/site-packages (from pyvips) (1.5.5)
Requirement already satisfied: pycparser in /home/john/vips/lib/python3.11/site-packages (from cffi>=1.0.0->pyvips) (2.21)
Installing collected packages: pyvips
  DEPRECATION: pyvips is being installed using the legacy 'setup.py install' method, because it does not have a 'pyproject.toml' and the 'wheel' package is not installed. pip 23.1 will enforce this behaviour change. A possible replacement is to enable the '--use-pep517' option. Discussion can be found at https://github.com/pypa/pip/issues/8559
  Running setup.py install for pyvips ... done
Successfully installed pyvips-2.2.1