CHANGES:
- Dns.Dnskey: provide to_string and name_key_to_string (@hannesm, @dinosaure,
#356 - fixes #355) - BREAKING: Dns.Dnskey remove pp_name_key (unused, irritating, #356)
- BREAKING Dns_certify_mirage.retrieve_certificate use separate dns_key_name
and dns_key arguments, avoid string decoding in that function (#356)