Wrap all loggers used by job, extractor, downloader, and postprocessor
objects into a (custom) LoggerAdapter that provides access to the
underlying job, extractor, pathfmt, and kwdict objects and their
properties.
__init__() signatures for all downloader and postprocessor classes have
been changed to take the current Job object as their first argument,
instead of the current extractor or pathfmt.
(#574, #575)
This allows for stuff like "{extractor.url}" and "{extractor.category}"
in logging format strings.
Accessing 'extractor' and 'job' in any way will return "None" if those
fields aren't defined, i.e. in general logging messages.
- safeprint() was used to print values which might have caused a
UnicodeEncodeError, but that is no longer necessary (0381ae5)
- errors are now handled via logging output (f94e370)
