Update api_spec.md to match functionality implemented

Via:
 * https://github.com/PowerDNS/pdns/pull/1460
 * https://github.com/PowerDNS/pdns/pull/1438
 * https://github.com/PowerDNS/pdns/pull/1423
Merge pull request #5 from tuxis-ie/master

Update api_spec.md to match functionality implemented