- Replace the old logging mechanisms with a leveled one. This is
important as authboss needs to start saying a lot more about what's
happening in the Info log, which will end up like Debug but that's
okay.
- Replace the error handling mechanisms with something different. This
allows people to define their own error handlers.
- Having the default logger set to nil was troublesome because some errors
are hard to detect without a logger. This falls under "sane default"
changes and so should be made.
