Check that lints roxygen and md

[katrinabrock]

In particular problems that plague me that I'd love to have an automated check for:

• Improperly formatted md lists e.g. omitting the empty line before the list which cause the list to be misformatted in pkgdown and elsewhere.
• Markdown in roxygen without Roxygen: list(markdown = TRUE) or vice versa and/or a mix of markdown and Rd syntax.

For markdown syntax, I've used this packages vscode extension: https://github.com/markdownlint/markdownlint . It catches the above case, but also is maybe a little overly strict out of the box so could use some tuning.

For roxygen, there is a roxygen lint package: https://openpharma.github.io/roxylint/index.html I haven't used it before. It doesn't look like it checks the case I mentioned above, but maybe useful as a framework to add whatever checks are deemed appropriate.