a `nimibook / license` module

[pietroppeter]

thanks to #86 we now have a license page that lists licenses for all assets bundled with nimibook.
we could make the text of the list of licenses a constant in a new nimibook / license module so that other project using nimibook (such as owlkettle where this issue originated, see #80) can reuse that and be updated when content is updated.

[PhilippMDoerner]

Does this include a way for the user to add their own tuple[assetName: string, licenseName: string] list to display on top of the ones nimibook will add?

Maybe even split them out, one section for nimibook related licenses, a second section on the same page for all project-specific related licenses?

[pietroppeter]

Mmh, initially I was thinking of a single const string of text, but now that you mention it we could have also tuples for each license asset (name of asset, name of license but maybe also url?). I would not want this too complicated, anyway it is easy for the user to customize.