To protect against DNS spoof attacks, we now check that the questions
in incoming responses match the questions in the request we sent out.
Suggested by @zecke in #10.
- Break out request building into a DNSRequest class.
- Break out response parsing into a DNSResponse class.
A DNSRequest contains one or more DNSQuestion objects.
A DNSResponse contains all the DNSQuestions asked, and a DNSAnswer
object for each answer.
