Feature/96 97 issues

[smarie]

This Pull request fixes #96, fixes #97
Changes are in src/mkdocs_gallery/gen_single.py

I also had to update the CI workflows including nox sessions, for CI to run smoothly.

[smarie]

@schlegelp could you checkout this branch, run pip install . while having your work environment activated, and let me know if it solves the two issues ? Indeed the test harness of this project is quite small so I prefer to double-check.
Thanks !

In the meantime I am trying to solve an issue of package versions compliance between mayavi, numpy and configobj
EDIT: done, all CI jobs pass. Waiting for your confirmation that this has the expected behaviour concerning metadata of the readme pages.

If you would like to propose something different, feel free to propose a code to replace what I did in src/mkdocs_gallery/gen_single.py

[smarie]

I ended up modifying the built-in example gallery to include custom metadata, it seems to work.
waiting for CI to pass and then I'll release

[schlegelp]

Left a comment and another request in #96!