21.5.0

I didn't expect to make this release but @aucampia and @airwoodix contributed features that I'm sure will excite many users, so here's Santa Hynek 🎅 with a surprise release.

Changes:

• Added the structlog.processors.LogfmtRenderer processor to render log lines using the logfmt format. #376
• Added the structlog.stdlib.ExtraAdder processor that adds extra attributes of logging.LogRecord objects to the event dictionary. This processor can be used for adding data passed in the extra parameter of the logging module's log methods to the event dictionary. #209 #377
• Added the structlog.processor.CallsiteParameterAdder processor that adds parameters of the callsite that an event dictionary orginated from to the event dictionary. This processor can be used to enrich events dictionaries with information such as the function name, line number and filename that an event dictionary orignated from. #380