Add linter to detect broken links
Why is this change being made?
Problem
The new Handbook doesn't have a linter that verifies that links are valid. It leads to increase of broken links number.
Solution
As a quick fix, I migrate the old Handbook ruby linter to the new Handbook project.
It currently applies limited validations only, but it's better than nothing. As a follow-up, it can be improved or swapped with a different solution.
Edited by Vasilii Iakliushin