- knot_rrset_copy now returns pointer

- knot_rrset_create_rr removed, only way to insert RR into rrset now is
  when you already have RDATA, so that we never create RRSet that is not
sorted.
- rr.h doxygenated, functions moved around a bit.

 - merging can now be done directly using knot_rrs_t

 - tests are passing, however some work is still pending, namely storage
   of additionals for freeing.
 - removed some obsolete node API functions

- removing and adding already existing record
- leak solved, but need to move old a new data lists from
  zone_contents_t

- only basic functionality with leaks

- Lost my temper with the direct changes, rewritten DDNS to only
  changeset creation, application will be the same as usual.
- Will not work now

updates.

- DDNS and changeset application will not work now, but it wouldn't work
  before either

- some cleanup and fixes as well, namely simplified RR creation during
  zone load (no malloc)

- RRSet copies removed, packet now stores rrsets directly (structure is
  copied, but copy is shallow)

- use rrset initialization macro instead, or create rrset explicitely

- kept RRSet copies somewhere (node has to create them now)
- replaced knot_rrset_t with knot_rrs_t elsewhere
- semantic checks simplified

Prior to this change, non-apex DNSKEYs were not signed and invalid NSEC
records were generated for these nodes.

- Will leak
- Untested

The config.h is now implicitly included using -include option of the
compiler. After this change, config.h need not be placed at the first
position in all source files.

Was leaving RRSIGs of removed NSEC3s in the zone, if some NSEC3
changed.

- RR insertion function now returns zone RRSet.
- Removed reduntant zone contents / node API functions
- Cleanup.

- Fixed mismatched variables, do not use call directly in for loops.

- Removed rrset->rdata_indices, RDATA lengths are now stored inline together with RR's TTL
- Added function to get RR's TTL - TTL of the whole RRSet can still be obtained, but it will default to the first RR's TTL or 0
- Renamed few RRSet functions, removed a few too - the file still needs a cleanup and function reordering
- Special handling for RRSIGs during AXFR-out no longer needed (yay)

- RRSIGs from node are added to rrinfo section.
- When putting RRSIGs for each section, proper RRSIGs for each RRSet are syntesized and later freed.

closes #204

Each RRSet that is stored in node, even if it's only a placeholder,
must be counted because the array of RRSets is indexed by this
count.

Changed condition in NSEC chain generation - the NSEC should be
dropped also in case where there are NSEC and some placeholder
RRSets in the node.

refs #210

In some cases, NSEC3 records were generated for empty non-terminals
that were subsequently deleted after applying the DNSSEC changeset.

refs #210

Was causing problems when RRSet was removed but its RRSIG remained
in the zone.

issue #1