Add pyproject.toml to avoid pre-installs with pip

[AxelHenningsson]

An attempt to make ImageD11 installable with pip in a clean environment, without any prerequisites.

On a windows 10 using conda (as below) this installs with pip and passes pytest without any pre-installed packages such as numpy or the like. To replicate:

 conda create -n dev_ImageD11 python=3.8
 conda activate dev_ImageD11 
 git clone https://github.com/FABLE-3DXRD/ImageD11.git
 cd ImageD11
 pip install -e .
 conda install pytest
 pytest

[jonwright]

I will merge as is but I have in mind that pytest should be coming in somehow automatically too?

[AxelHenningsson]

Yeah I was surprised that the CI does not trigger tests on a pull requests. I have mostly used GitHub actions to do CI stuff, so don't exactly know how the .circleci file works with tests in ImageD11.