Split NDEBUG to NDEBUG (asserts) and NOVERBOSELOG (verbose logging); rename all related symbols to use VERBOSE instead of DEBUG

It causes lots of line changes, but it would be confusing to keep the
current state over long term.

The cookie module could segfault due to the `opt` pointer not being
initialized when no EDNS was sent in the incoming request.

if the score is known (and not glued), the retry
rate is <avg(rtt), 250ms>

if the NS score is unknown or worse than 250ms,
it is always retried at this rate

all other servers in the list use default rate

Consequently, there's no use for worker_reserve in the header.

timeouts over TCP when <n> first nameservers timeout over UDP as
previously the TCP would connect again to the first and only the
first nameserver in task->addrlist.

This would need to be ultimately fixed in TCP Fast Retransmit.

The control structure is part of the resolver context.

Use ENABLE_cookies=yes variable to compile functionality.

Cookies are not stored in separate cache.

the TLS sessions now bypass the usuall event loop asynchronous iops
this is because the whole operation is synchronous right now, and
implementing asynchronous send operations would require TLS session to
restart write events on the event loop and making sure the "on complete"
callback is called eventually