this fixes a bug when a text-declared type wasn’t reused and LJ eventually segfaulted in ffi.new after a lot of redeclarations

fixes #41

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

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 #16

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

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

this is useful when you need to issue several subrequests before
continuing with the current query, resuming is not supported yet, so it
will requery after the subrequests complete

current processed query is always in `request->current_query`

i.e. if the user doesn't set the cache, it will be applied later
if he sets it, it will stay

this is going to be needed for issuing multiple timed queries + fast
retry

effectively enables/disables usage of given IP protocol
for subrequests (the server can still listen on these)

the key is now stored in a format friendly to prefix search, the values
also contain one more 16bit field to store rank of the data (to be
utilised later)