Add CDS/CDNSKEY record types

[coreyhaines]

This adds record types for CDS and CDNSKEY as defined in RFC7344.

This was a straightforward enhancement, copying the code for DS/DNSKEY records, as according to the RFC they are the same:

The wire and presentation format of the Child DS (CDS) resource record is identical to the DS record [RFC4034]. IANA has allocated RR code 59 for the CDS resource record via Expert Review.

and

The wire and presentation format of the CDNSKEY ("Child DNSKEY") resource record is identical to the DNSKEY record. IANA has allocated RR code 60 for the CDNSKEY resource record via Expert Review.

Changes

• [x] dnssec_tests.hrl - wiresamples.txt (copy existing ds and dnskey tests)
• [x] dns_records.hrl : record type
• [x] dns_terms.hrl : macros
  • [x] DNS_TYPE_CDS
  • [x] DNS_TYPE_CDS_NUMBER
  • [x] DNS_TYPE_CDS_BSTR
  • [x] DNS_TYPE_CDNSKEY
  • [x] DNS_TYPE_CDNSKEY_NUMBER
  • [x] DNS_TYPE_CDNSKEY_BSTR
• [x] dns.erl : typespec + encode/decode functions
  • [x] Add to rrdata type
  • [x] Add decode that delegate to decoding CDS/CDNSKEY
  • [x] Add encode that delegates to encoding CDS/CDNSKEY
  • [x] Add to type_name function
• [x] dns_record_info.erl : information functions for the type
  • [x] fields
  • [x] size
  • [x] atom_for_type
  • [x] type_for_atom