Allow for adding and setting mkdocs style header entries

[PlasmaHH]

I am trying to integrate sphinx based documentation into an existing mkdocs project. This extenion is getting me really far already, but there are a couple of things that could need polishing, in this issue its about the mkdocs header.

mkdocs supports a variety of header fields, all at the start of the .md file like:

Title: title as shown in the navbar
hide: toc

and it would be great if we could somehow provide this extension with a dict (or maybe a hook or so) to output these things. In my use case I would like to have the hide: toc part in every file.

The title part however would be most useful if there was some format/template thing possible so I can e.g. say title: {fullname} (or whatever the variable would be) so it creates Title: name_of_function whereas the heading is currently maybe ### name_of_function( x: str = "" ) -> None (which would be too cluttered for the title in the navbar)

[liran-funaro]

Thank you so much for taking the time to share your feedback and suggestions!
While my bandwidth for implementing new features is limited at the moment, I truly appreciate your initiative and would be happy to review and merge a pull request if you'd like to contribute to this enhancement.