This implements a basic validation schema using a checklist. We try
every pair at least maxTries, and mark it as failed if we don't get a
success response after that many requests. Once we get a success
response, we check if it belongs to the best candidate available so far,
if it does we nominate it, otherwise we continue.
Also, after a given timeout, if no candidate has been nominated, we
simply choose the best valid candidate we got so far (if no candidate is
valid, we mark the connection as failed).
Finally, the nomination request also has a maximum of maxTries, we mark
the connection as failed if after that many attempt we fail to get a
success response.
This change will allow us to have custom logic and members
per interface type. Relay candidates will have a completely different
read loop, and candidate specific state.
Relates to #47
Some constants were being incorrectly generated using 2^N (XOR)
instead of 1 << N. This resulted in incorrect candidate priorities
being used to evaluate candidate pairs.
Resolves#14.
