kresd has --tls/-t by analogy with --addr/-a where the daemon opens
the socket itself.

This changeset adds equivalent functionality for inherited sockets:
--tlsfd/-T by analogy with --fd/-Sa

when whole interface is passed and some of the addresses are not bindable,
the daemon will print them, but will continue to bind to the rest of the
addresses

fixes #80

forks are connected with IPC pipes to process
group leader and can execute expressions on its
behalf. so running commands over all workers
is easy now:

> hostname() -- single
localhost

> map 'hostname()' -- all
localhost
localhost
localhost

fixes #73 small leak in cleaning up per-socket
mempool on daemon exit

* 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

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

this is not going to be backwards compatible change, but it will be the first tagged libknot release sufficient for resolver