dnssec-checkds CDS support, and other improvements
* Use `dnssec-dsfromkey -p` to work out what the delegation records should be, based on CDS records. * Better error checking for failures by `dig`. * Add a --every mode for checking all the parent name servers. This is for extra protection against long propagation delays. * Add a --quiet mode to avoid unwanted cronspam. There is still output if something unexpected happens, so --quiet mode is better for cron jobs than just redirecting the output. * Explain how this tool relates to other tools. The current strict consistency logic was introduced when SHA-1 was deprecated, but it wasn't documented. The manual has now been updated. (Users who want checks based on validation semantics should use something like zonemaster or dnsviz instead.)