Check for the most common markdown format errors

[cansavvy]

I make the same markdown formatting errors all the time. ALthough I don't think such a check should be required, it could be used as a warning if I can get it honed in enough on the errors.

Basically this would be an additional optional check set used by ottr to catch markdown formatting errors like those described here:

https://www.markdownguide.org/basic-syntax/