Consider adding an external link checker

[jaredkrinke]

As long as it doesn't slow down reloads. Maybe make it optional?

[jaredkrinke]

Even with 20 concurrent requests, checking all external links takes several seconds for my fairly small site (which builds and checks in less than a second without external link checking).

I'd like to avoid caching anything to disk because then there'd need to be policies around invalidating the cache, etc. Results could be cached in memory to speed up rebuilds in the watch/serve scenarios, but I think the only reasonable design is to make this opt-in behavior.

[jaredkrinke]

Because this can be slow, it should also have some logging to indicate progress.

[jaredkrinke]

Possible design:

• Opt in
• Asynchronous (and won't prevent the site from being built)
• Periodic status
• Abort if a new build is kicked off
• Cache external resource results in-process (and never invalidate the cache)

This seems handy, but is it worth spending time on a feature that is not used by default?

[jaredkrinke]

Added a FAQ entry with an example of using a separate tool for checking external links:

https://jaredkrinke.github.io/md2blog/posts/faq/checking-external-links.html

With that in place, I'm deferring this work to a future release.