Improve markdown highlighting in the docstrings

[rrudakov]

Follow up #78

• package-lint is disabled
• added more queries for markdown syntax in the docstrings

---

Before submitting a PR mark the checkboxes for the items you've done (if you
think a checkbox does not apply, then leave it unchecked):

• The commits are consistent with our contribution guidelines.

• You've run M-x checkdoc and fixed any warnings in the code you've written.
• You've updated the changelog (if adding/changing user-visible functionality).
• You've updated the readme (if adding/changing user-visible functionality).

Thanks!

[rrudakov]

Finally all the checks are green haha.

[bbatsov]

This was fast! Thanks!