Add `jupyter-book create --cookiecutter` (thanks to [@TomasBeuzen](https://github.com/TomasBeuzen))
: This adds a `--cookiecutter` option to `jb create`, to allow users to use the [Jupyter Book cookiecutter](https://github.com/executablebooks/cookiecutter-jupyter-book) to create a book template.
The cookiecutter is suitable for more advanced users that want to create a ready-to-go repository to host their book that includes pre-populated metafiles such as README, LICENSE, CONDUCT, CONTRIBUTING, etc., as well as GitHub Actions workflow files.
### Fixes 🐛
This release contains numerous improvements, to the documentation and code, to address issues noted by you guys:
- Fix issues with single document builds (e.g. pdflatex) and relative path resolutions
- Ensure `sphinx-book-theme` is loaded on PDF builds (to allow the use of the `margin` directive)
- Allow execution `timeout: -1` and `execute_notebooks: off` to be valid in the `_config.yml`