Merge branch 'kzonecheck_clarify' into 'master'

doc/man/kzonecheck.1in

doc/man_kzonecheck.rst

src/knot/events/handlers/refresh.c

src/knot/zone/semantic-check.c

src/knot/zone/semantic-check.h

src/knot/zone/zone-load.c

src/knot/zone/zonefile.c

src/knot/zone/zonefile.h

src/utils/kzonecheck/main.c

src/utils/kzonecheck/zone_check.c

src/utils/kzonecheck/zone_check.h

tests/knot/semantic_check_data/cdnskey.cds

tests/knot/semantic_check_data/cdnskey.delete.both

...s/knot/semantic_check_data/cdnskey.delete.invalid.cdnskey

tests/knot/semantic_check_data/cdnskey.delete.invalid.cds

tests/knot/semantic_check_data/cdnskey.invalid

tests/knot/semantic_check_data/cdnskey.invalid.param

tests/knot/semantic_check_data/cdnskey.nocdnskey

tests/knot/semantic_check_data/cdnskey.nocds

tests/knot/semantic_check_data/cdnskey.nodnskey