the query flags were cleared too early, and the rec never
retried if the NS had ipv6 addresses, but all were bad

this fixes an issue when nameserver responds with AA=0 and authority
of a CNAME target (which is in current bailiwick)

DNS 0x20 https://tools.ietf.org/html/draft-vixie-dnsext-dns0x20-00
is a way to add more randomness into queries to make spoofing tougher
this implementation provides up to 32 bits of randomness to QNAME,
which is more than enough for most names (it is possible to add a
maximum of 1 bit of entropy per alphanumeric character, so it's not very
efficient with shorter names)

fixes #27

libuv doesn't do connected UDP sockets, so we can't get ICMP unreachable
otherwise

before root hints were hardcoded to the resolver,
now they are present in form of a cut in the resolution
context, and the modules can add/remove/replace them
on the fly

fixes potential cache key oob write

also some cleanup and version bump to Q2

previously a CNAME RR could be merged as a queried type RR, leading to failed cache lookups as ‘expired’

previously if NS had no A/AAAA records, they we’re looked up in subrequests, after that a new NS was reelected (possibly preferring another unknown), now it stays true to the NS of choice and changes only if it is unuseable

the cache_peek() api was reworked to return an error code instead, from this the caller can tell whether the record is present (but expired) or missing. this save a secondary CNAME lookup in case the original record was just expired

this LRU-like cache tracks lame nameservers, unresolvable
nameservers (to not waste resources in trying to resolve them),
and possibly other features (extension support, …)