Test on-site links to sections to see if they exist

[a2sheppy]

When there are links to pages on MDN which exist, but to sections on those pages which don't, we should put up a warning.

[SebastianZ]

Good point! Though I'd say that's an error rather than a warning, no?

As a first step, I'd say to only check anchor links on the current page.
Checking other pages requires asynchronous handling, which needs to be implemented first and should be done in a separate issue.

Sebastian

[a2sheppy]

Yeah, should be an error.

-- Sheppy

[Elchi3]

Re-filed as mdn/doc-linter-rules#18