this module allows to rewrite address ranges in answers to different address ranges specified in configuration

this allows daemon to try other NSs for fast retransmit if the best chosen NS doesn’t respond within time limit

instead of single I/O request per step, the daemon now retries
all addresses in the selection with 300ms timeout between tries.
there are len(list) + len(list)/2 tries

the idea is to reduce latency when UDP request doesn't punch through,
or some NSs are overwhelmed/faulty

RRs may be touched after resolution completion, this copies RR from
temporary per-recv buffer to answer, which is persistent for the whole
duration of request

if the library or daemon is compiled with address sanitizer, objects in
freelists are poisoned to detect use-after-recycle errors
it is not currently used in the library, as there are no freelists

refs #33

refs #16

this is Unbound's 'forward-zone' on steroids

the library is able to resolve query in stub mode (no referral chasing,
zone cut lookup) if asked to
validator turns off for stub queries, validating stub is NYI

thanks to Pieter Lexis and Peter van Dijk from PowerDNS for discovering this.

the RFC4035 M < S < N stands if the S isn’t after the last name in the zone, this is indicated by M > N, proving that the next of the last name is the first name; if the S is after M, then it proves it’s non-existence

thanks to Pieter Lexis and Peter van Dijk from PowerDNS for discovering this!

resolved() returns true if current query is resolved (i.e. authoritative)
final() returns true if current query is resolved and is not a subrequest (has no parent)

as the libknot packet interface disallows out-of-order packet
writes, authority and additional records must be written after
the answer is complete; records in the rr arrays will be written to final answer during finalization