Add new setting: disable unicode in slugs.

[corentinbettiol]

Description

Add optional BLOG_UNICODE_SLUGS setting (default is still allow_unicode=True when generating a slug).

Update black version in .pre-commit-config.yaml in order to make this commit.

References

Fix #707.

Checklist

• [x] I have read the contribution guide
• [ ] Code lint checked via inv lint
  • never seen the end of the command, seems to output errors for hours, may be broken ?
• [x] changes file included (see docs)
• [x] Usage documentation added in case of new features
  • added a simple setting var, should be auto-added in the doc during build
• [ ] Tests added
  • may add a test later when I have more time + when all the tests will be fixed

[yakky]

@corentinbettiol thnaks for the PR, I think some mention in the docs is needed to bettere communicate this option

I will work on the test suite to make it work again, in the meantime

[yakky]

Thanks your contribution @corentinbettiol , I merged this with #727 to ease porting to updated develop branch

[corentinbettiol]

Thanks!