Links to RFCs point to tools.ietf.org instead of the current datatracker.ietf.org URLs

[auerswal]

Links to HTML renderings of RFC documents point to tools.ietf.org. They are automatically redirected to datatracker.ietf.org, because in the IETF there is the intent, and ongoing work to implement this intent, to retire tools.ietf.org.

The redirect is a simple rewrite from, e.g., https://tools.ietf.org/html/rfc1034 to https://datatracker.ietf.org/doc/html/rfc1034 (s/tools\.ietf\.org/datatracker.ietf.org\/doc/).

Changing all those URLs touches many lines of many files and might thus interfere with open pull requests:

$ git grep -cF tools.ietf.org
auth.md:5
basic.md:15
optional.md:11
tdns/ext/nlohmann/json.hpp:11
tdns/intro.md:2

I'd be happy to prepare such a pull request if you'd like me to.