- docs: fix cache.current_* since long ago d5272b4b
- don't allow "cache.foo = 'bar'" for abitrary foo
- restore cache['nic.cz'] after b31bad2ccf while not breaking completion
- #cache won't work on lua 5.1, so remove it

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

... but don't raise any kind of error.
The lua function `verbose()` behaved reasonably already.
It doesn't warn, but docs for the function do mention `NLOGDEBUG`.

... and avoid returning a negative number.

Fixes https://gitlab.labs.nic.cz/knot/resolver/issues/93.
API of a KR_EXPORT function is changed, so ABIVER is bumped.

Based on [issue 28](https://github.com/CZ-NIC/knot-resolver/issues/28), we were able to boost kresd performance running in a Docker container on DockerCloud by nearly 100% by binding to a single interface:ipaddress. It might be handy for other users to know.

As noted in #94, it feels natural to call it like:
``net.listen({net.lo, '192.168.1.1'})``
Also, minor fixes were done in that function and corresponding docs.

there are cases where switches or middle-boxes
block DNS/UDP answers >512 octets completely,
this gives user an option to mitigate that.
however, there are authoritatives serving
large answers that don't support TCP, so it's
a compromise as always

there are cases where switches or middle-boxes
block DNS/UDP answers >512 octets completely,
this gives user an option to mitigate that.
however, there are authoritatives serving
large answers that don't support TCP, so it's
a compromise as always

this allows for efficient variable-interval
running events, so that the timer doesn't have
to be closed and recreated for each iteration

this allows embedding other event loops or just
asynchronous events triggered by socket activity.
this is required for things like cooperative
HTTP server, monitoring endpoint or remote
configuration daemon/controller

this change introduces new API for cache backends,
that is a subset of knot_db_api_t from libknot
with several cache-specific operations

major changes are:
* merged 'cachectl' module into 'cache' as it is
  99% default-on and it simplifies things
* not transaction oriented, transactions may be
  reused and cached for higher performance
* scatter/gather API, this is important for
  latency and performance of non-local backends
  like Redis
* faster and reliable cache clearing
* cache-specific operations (prefix scan, ...) in
  the API not hacked in
* simpler code for both backends and caller

* daemon now processes messages over TCP stream
out-of-order and concurrently
* support for TCP_DEFER_ACCEPT
* support for TCP Fast-Open
* there are now deadlines for TCP for idle/slow
streams (to prevent slowloris; pruning)
* there is now per-request limit on timeouts
(each request is allowed 4 timeouts before bailing)
* faster request closing, unified retry/timeout timers
* rare race condition in timer closing fixed

the daemon has now three modes of strictness
checking from strict to permissive.
it reflects the tradeoff between resolving the
query in as few steps as possible and security
for insecure zones

new trust anchors variables:
* trust_anchors.hold_down_time = 30 * day
* trust_anchors.refresh_time = nil
* trust_anchors.keep_removed = 0

these could be used to control how often should
root trust anchors be checked and how many removed
keys should be kept in log (0 by default)

Signed-off-by: Tomas Hozza <thozza@redhat.com>

addition to previous generic socket activation

fixes #11

daemon can accept existing fds on command line,
thus supporting process managers like circus or
upstart. a tiny supervisor script is attached