Add rule to check for file naming about markdownlint

[DavidAnson]

To be clear, you are referring to the names of the Markdown files that are parsed for content, right? If so, this feels a bit on the edge of what I think a Markdown linter should do. But I will think about this more.

[pascalberger]

Yes, I was referring to the *.md files. I see the point that this is not a typical use case for a linter, since it is no longer about the content. On the other hand, considering a repo containing some source and Markdown documentation, it still has to do with the Markdown part :)

[DavidAnson]

Got it.

What about something like this instead: https://www.npmjs.com/package/gulp-check-file-naming-convention

Or maybe:
https://www.npmjs.com/package/check-filename

[pascalberger]

Thinking a little bit more about it, doing these checks outside might be the better solution than duplicating existing functionality here.

[DavidAnson]

Great.