Old system was using manual string formatting for log messages.
This caused issues with common operations like exception logging
because often they need to be handled differently for Py2/Py3
compatibility. In order to unify the effort:
- All logging is changed to `logging.level(msg, arg1, arg2)` style.
- A `SafeLogger` is implemented to auto-decode exceptions properly
in the args (ref #1403).
- Custom formatters were overriding useful logging functionality
like traceback outputing (ref #1402). They are refactored to be
more transparent. Traceback information is provided in `--debug`
mode for `read_file` errors in generators.
- Formatters will now auto-format multiline log messages in order
to make them look related. Similarly, traceback will be formatted in
the same fashion.
- `pelican.log.LimitFilter` was (ab)using logging message which
would result in awkward syntax for argumented logging style. This
functionality is moved to `extra` keyword argument.
- Levels for errors that would result skipping a file (`read_file`)
changed from `warning` to `error` in order to make them stand out
among other logs.
- Small consistency changes to log messages (i.e. changing all
to start with an uppercase letter) and quality-of-life improvements
(some log messages were dumping raw object information).
Drop duplicates logs.
Allow for logs to be grouped, enforcing a maximum number of logs per group.
Add the LOG_FILTER setting to ask from the configuration file to ignore some
logs (of level up to warning).
