Apparently the clever hack for logging in on_error was not so clever
after all. If logging isn't configured, by the logging modules
definition of not configured, which is root logger not having an
Handlers attached, it will call logging.basicConfig(). Which messes up
setups that define handlers for other loggers than the root logger.
Going directly to the root logger rather than using the broken
convenience methods for logger is not an option either, as logger before
Python 3.2 does not have lastResort on the root logger, and prints an
error when invoked without any handlers.
Resolve by printing tracebacks to stderr by default in on_error.
Documented the new way of listening to events as well the new
events that could be listened thanks to the recent refactor.
Also uses the versionadded directive to document when something new
is added to the library.
Change the description of on_error to reflect that exceptions are logged
and not output by default. Add a note about not configuring logging
causing exceptions to be silently ignored in handlers in the API. And
add some more explanations and a simpler configuration example to the
logging description.
