the server responds with edns0 if the client requests it,
it also uses DNSSEC for queries if DO=1

the obtained records are not however validated

if the server doesn’t understand edns0, replies with
notimpl, formerr or sends bad badly formed response,
we try basic dns query (ns0.rbsov.bbc.co.uk)

previously cryptolib random function was used to generate message id,
this works well but it is slow especially when the entropy is low,
replaced with cryptographically safe prng ISAAC

the ccan directory is going to be used in the future, as it's include
structure makes it easy to embed C snippets instead of reimplementing
them

the encloser might exist and contain valid data, the resolver would return wrong records in this case

instead of keeping just random NS and address,
it keeps a map of nameservers => {addresslist}

this allows scoring and correct NS election, fallback
and evaluation

this fixes resolution of multi-level queries, when a side query
encounters a nameserver that requires address resolution

as glue (or any additionals) are NOT cached

- cache is now fully optional, resolution works without cache as well
- proper mempool per each request, not mixed
- zone cut resolution doesn't need any per-context memory
- now it's possible to do qname minimization
- rplan keeps tabs on resolved queries
- added documentation etc.

- correct processing of NS records in the authoritative answers