docs: recursor/running: cleanup

Mark all config vars bold, all commands/parameters preformatted,
remove double escaping.
docs: recursor/running: add new(er) commands
root MX test
test NS and CNAME pointing at the root
no fancy-records in tinydns generate-data.sh
output varies between versions
mydnsbackend: fix types pointing at root
lmdbbackend: fix types pointing at root
README.md: point people directly at the new docs
Document AXFR-SOURCE domainmetadata option
Merge pull request #1942 from rubenk/update-readme

README.md: point people directly at the new docs
Merge pull request #1943 from rubenk/document-axfr-source

Document AXFR-SOURCE domainmetadata option
Only log remote nameservers

Skip the A/AAAA records.

Previously, we would log:
Unable to find backend willing to host example.com for potential supermaster x.x.x.x. 4 remote nameservers:
test1.example.com
test2.example.com
x.x.x.x
x.x.x.y
Add rping to the pdns_control manpage
Add documentation links to systemd unit
Merge pull request #1947 from rubenk/document-rping

Add rping to the pdns_control manpage
Merge pull request #1930 from mind04/test

root MX test
Merge pull request #1949 from rubenk/add-docs-to-systemd-unit

Add documentation links to systemd unit
Merge pull request #1927 from zeha/reccontrol-docs

Update docs/recursor/running
Merge pull request #1946 from rubenk/only-log-nameservers

Only log remote nameservers