Merge branch 'ddns' into development

Knot.files

libknot/Makefile.am

libknot/nameserver/name-server.c

libknot/nameserver/name-server.h

libknot/packet/packet.c

libknot/packet/packet.h

libknot/rrset.c

libknot/rrset.h

libknot/updates/changesets.c

libknot/updates/changesets.h

libknot/updates/ddns.c

libknot/updates/ddns.h

libknot/updates/xfr-in.c

libknot/util/debug.h

libknot/util/descriptor.c

libknot/util/descriptor.h

libknot/util/error.c

libknot/util/error.h

libknot/util/utils.c

libknot/util/utils.h