Add rule(s) to enforce certain link rules

[braebot]

Add rules to detect and error when found:

1. No http links,
2. No links include text from a set of given regexes,
3. No relative links, such as ../path, path. Only allow absolute links, such as /path.

Note: this is similar to those that would be found when crawling a site. However, it is best when caught earlier in the process with markdownlint.

[DavidAnson]

Based on your scenarios, a single rule that runs a user-configurable RegExp against the link destination seems sufficient.

[braebot]

Yes, that would be sufficient!

[sanmai-NL]

Another use case: https://github.com/webhintio/hint/issues/4137.