Implement connection tracking and basic exception handler.

[amarburg]

Zero-th order update which should reduce segfaults from Oculus.

This addresses two core problems:

1. When the IP address for the sonar is provided (as opposed to relying on auto-detection), "isConnected()" was using a function which did not actually indicate if the socket was connected (it indicated that the socket was "open" but did not validate IP address, port, etc). Instead, we track this state manually. This prevents the code from erroneously sending data to a non-existent (or not powered on) destination.
2. When you send data to a non-existent destination, asio throws an exception, which wasn't being caught. Added a highest-level catch.

The remaining failure point is that we still don't have a higher-level retry loop, so it won't catch if the sonar was off, then was turned on and became available. Or was on, then turned off, then on again. TBD.

Current behavior is:

• IpAddress provided to driver, but sonar is not on. Outcome: Library goes into an infinite wait (Waiting for data on a closed socket that will never open)
• Sonar is connected (either through autodetect or manually specified), then turn off. Outcome: Library goes into an infinite wait (Waiting for data on a closed socket that will never open)

[amarburg]

I've expanded the scope of this PR; it now includes "real" error checking for disconnects, tx/rx errors and timeouts. The library largely does not do anything autonomously, instead relying on onDisconnect and onTimeout callbacks for the userspace code to coordinate a response.

This works for both "auto" and specified-IP modes, although finding the right amount of debug output was a challenge -- right now we can't distinguish "the connection was lost (the sonar dropped out)" from "I (re-)tried but couldn't reach the sonar". In the former case you want some log output. In the latter, you might prefer not to have continuous updates as it retries.