Mkdocs-monorepo-plugin

- Don't run on_serve if on_config was skipped

- Add support for wildcard include statement

- Fix `No module named 'slugify'` error when installing in mkdocs environments.

- Allow `mkdocs.yaml` in addition to `mkdocs.yml`
- Drops support for Python 3.5 (because the minimum `mkdocs` version which
supports the above feature no longer supports it).

- Allow inclusion of sub-docs `mkdocs.yml` even if its name isn't URL-friendly.
Works by slugifying non-URL friendly names. (58)

- Fixed bug where URLs in an included `mkdocs.yml` were prefixed by the `site_name` and thus did not support absolute URLs.