Add cds record type

[coreyhaines]

Part of implementing CDS/CDNSKEY

This adds the record type for CDS

This includes the following steps:

• [ ] dnssec_tests.hrl - wiresamples.txt . Figure out how to use this for cds?
• [x] dns_records.hrl : record type (same as DS record)
• [x] dns_terms.hrl : macros
  • [x] DNS_TYPE_CDS : ?DNS_TYPE_CDS_NUMBER
  • [x] DNS_TYPE_CDS_NUMBER : 59 (per RFC 7344 3.1)
  • [x] DNS_TYPE_CDS_BSTR : <<""CDS">>
• [x] dns.erl : typespec + encode/decode functions
  • [x] Add to rrdata type
  • [x] Add decode that delegate to decoding DS
  • [x] Add encode that delegates to encoding DS
• [x] dns_record_info.erl : information functions for the type
  • [x] fields
  • [x] size
  • [x] atom_for_type
  • [x] type_for_atom

This can be merged, but should be deployed along with the other work from the project.