Merge branch 'tsig-keyfile' into 'master'

Knot.files

doc/man/kdig.1in

doc/man/knotc.8in

doc/man/knsupdate.1in

doc/man_kdig.rst

doc/man_knotc.rst

doc/man_knsupdate.rst

src/Makefile.am

src/knot/ctl/knotc_main.c

src/knot/ctl/remote.c

src/knot/ctl/remote.h

src/knot/dnssec/rrset-sign.c

src/knot/nameserver/process_query.c

src/libknot/internal/mem.c

src/libknot/internal/mem.h

src/libknot/rrset-dump.c

src/libknot/rrtype/tsig.h

src/libknot/tsig-op.c

src/libknot/tsig-op.h

src/libknot/tsig.c