IPv6 support and better portability

flick:ocaml-dns avsm$ more CHANGES
0.8.0 (2014-02-21):

• Use Ipaddr.V6 to restore IPv6/AAAA RR support.
• process_query now takes an output buffer so it doesn't have to
  overwrite the input buffer it just parsed.
• Add Travis continuous integration scripts.
• Regenerate with OASIS 0.4.1
• Split the dns.lwt into a portable dns.lwt-core that doesn't
  require Unix (from which a Mirage version can be built). The only
  change to existing applications is that Unix-specific functions
  have shifted into Dns_resolver_unix or Dns_server_unix, with
  the module types for PROCESSOR and CLIENT unchanged.