Templates for common jupyre-book settings

[cforssen]

(Following up on issue #7 in the tif285-book repo on gitlab)

Unique settings (such as the selection of chapters) are now included in each repo via the _config.yml _toc.yml files

However, several settings in _config.yml are universal. For example,

• shorthands used in the markdown files must be set in all _config.yml files.
• default values fo MYST substitutions used in the markdown files.
• default jupyter-book settings (most of these settings are used for all versions).

It would be good to figure out how to include that in the common content repo.

A simple alternative might be to have templates in the content directory.