Verify markdown output meets gfm and cmark using markdown linter

[clearbluejar]

For markdown, I haven't strictly checked the format. Generally, I am trying to make sure it works in most places, but primarily I manually test in github and gitlab. I will create another issue here to address the output, to make sure I follow some sort of standard. Likely I can use this tool https://pypi.org/project/pymarkdownlnt/ to verify my markdown output meets cmark and gfm. Again mermaid support will vary.

From #54