Initial update to suit R16 crypto changes

[aeden]

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