Hi there, enjoying use of the plugin. I anticipate this plugin will be a key part in making our documentation more concise and friendly.

I find myself frustrated by Jinja's ongoing challenges with consistent include indentation (#178). So, from the linked issue, I installed and began using this extension: https://github.com/stereobutter/jinja2_workarounds. The extension made it possible to have markdown-consistent indentation of template structure in the containing file.

To include the extension in the mkdocs-macros plugin I added the following to mkdocs.yml.

plugins:
  - macros:
      ...
      j2_extensions:
        - jinja2_workarounds.MultiLineInclude

This works exactly as expected, except that mkdocs now emits a warning on build because the option is "Unrecognised". We rely on the --strict flag to catch common issues from contributors, and don't want to turn it off, so we can't currently use the Jinja indentation extension in our documentation.

WARNING -  Config value 'plugins': Plugin 'macros' option 'j2_extensions': Unrecognised configuration name: j2_extensions

I see at line 119 in plugin.py the mkdocs-macros config schema is defined. Can the entry (j2_extensions, J2_STRING) please be added to the schema to allow users of your plugin to make use of Jinja extensions?

Thank you for your consideration, and for the awesome plugin!