Initial update to suit R16 crypto changes

Todo:
* need to document change of key format
* don't like code dupe between dnssec_tests:helper_pubkey_to_dnskey_pubkey
  and dns:encode_rrdata
* need to both test and add tests to make sure dns_record:serialise behaves
  the same
* helpers to/from mpints probably wouldn't go astray
* whitespace formatting is off cause somethings changed in my emacs conf