Experiments with zone freeing using dname table.

samples/example.com.zone

src/dnslib/dname-table.c

src/dnslib/dname-table.h

src/dnslib/node.c

src/dnslib/zone-dump.c

src/dnslib/zone-load.c

src/dnslib/zone.c

src/zcompile/zcompile.c