[x] I updated AUTHORS.txt and CHANGES.txt (if the change is non-trivial) and documentation (if applicable).
[x] I tested my changes.
Description
New features:
Trace template usage if env variable NIKOLA_TEMPLATES_TRACE is set.
Enable Jinja2 extensions via theme configuration.
Clarify template documentation: A parent template is not strictly needed.
Additional code improvements
helpful for those developing templates who actually read the code:
Added several typing hints and improved others.
A few code comments were added or improved.
Details
The code has three commits:
The first has no change, but the commit comment is the above notice, which I propose as the commit message of the entire commit once this is squashed on merge.
The second has only the changes to implement template usage logging.
The third implements ability to use Jinja2 extensions via theme configuration.
Pull Request Checklist
Description
New features:
Additional code improvements helpful for those developing templates who actually read the code:
Details
The code has three commits: