Check W3C link checker tool for improvement ideas

[mre]

I recently learned about the W3C link checker, a free tool available at https://metacpan.org/release/DHM/W3C-LinkChecker-5.0.0/source/bin/checklink
From a cursory look, the feature set is quite impressive. Maybe we can integrate the missing parts into lychee.

[mre]

Converting this issue to a discussion, since it doesn't track any kind of planned work but it's still valuable for future reference.