add pyproject.toml

[roipoussiere]

This pyproject.toml* is used to build the new cadquery2 package, using the ocp-vtk python package (which is based on #1048), which solves #153. I used poetry to build the wheel and publish it to PyPI.

One can install cadquery locally (in a virtual environment) with:

git clone https://github.com/CadQuery/cadquery.git
cd cadquery
python -m venv .venv
source .venv/bin/activate
pip install .

You may not want to merge it for now, but I wanted to share this pyproject.toml in some way and I was curious about the CI result.

*The specified file format of PEP 518 which contains the build system requirements of Python projects.

edit: ok the CI definitely needs the setup.py let's juts add the pyproject.toml.