Improve logging

At a very minimum, we should allow the user to change the severity at which we log – both client and transaction logs. Perhaps the 2 should continue to be separate loggers, with independent logging levels? Seems reasonable to me.

While doing this, we should attempt to get relevant info in the logs which we can use when tracking down issues. There is some of that now (logging calls that take an attempt_context for instance). Look at adding more as needed.