Nsupdate Update Fixed

Include Dir

closes #206

- packet is assembled in the correct order at the end
- packet is not sent until the 'send' command
- more descriptive logging

Sign Queries With Tsig

This fixes #161 among other stuff.

Simpler knot_pkt_reserve() API should be used instead.

- NOTIFY/SOAs now can be signed.
- Transaction security is checked.
- TSIG is checked before evaluating zone state.

Dig Flags

close #198

libknot split

Move server stuff from `src/libknot` to `src/knot`.

issue #1

issue #1

Current approach creates duplicate symbols when linking the library,
the simpliest solution is to make zscanner dependent on libknot.

issue #1

Packet Parse Compat

See the commit for rationale. This basically fixes a few compatibility issues when badly formatted query came and we treated it as NOOP.

If at least DNS header comes, treat it as a DNS packet; else ignore.
If query doesn't carry a question, reply with FORMERR.
If query carries more questions, reply with FORMERR.
If packet parsing fails, reply with FORMERR.
If there is a TC/RA/AA flag in query, accept it as soft error.