Refresh all filehandlers on named logger.

[JoeZiminski]

This PR resets the handlers on a named logger to empty so that repeated calls to fancylog respect the most recent calls arguments. This also adds a test to check the handlers are set as expected. Currently handlers are not removed from the
root logger as I'm not sure if it would have unexpected consequences. It does mean that this kind of example below can happen:

import logging
import fancylog

random_unused_filepath = r"random"

fancylog.start_logging(
    random_unused_filepath, fancylog, logger_name=None, log_to_console=True, log_to_file=False
)

logging.debug("written to console as `log_to_console=True`")

fancylog.start_logging(
    random_unused_filepath, fancylog, logger_name=None, log_to_console=False, log_to_file=False
)

logging.debug("still written to console because filehandler persists on "
              "the root logger even though `log_to_console=False`.")

But I think generally people will call fancylog.start_logging only once so not much of a problem, but makes sense to set for named loggers. Maybe in the docs in future the recommended way to use fancylog can be with a named logger as the behaviour is more predictable.

[adamltyson]

Maybe in the docs in future the recommended way to use fancylog can be with a named logger as the behaviour is more predictable.

👍