Rename T_APL to T_ADDRESSES

Fixes Github issue #15

Known DNS RRTYPE aliases can be found at
<http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml>
and `T_APL` conflicts with the `APL` RRTYPE, Address Prefix List, in
experimental RFC 3123.

Issue reported compilation issues on OpenBSD.

Instead, use `T_ADDRESSES`.