AS_SwiftLogHandler 2.0.0

• File handlers are reference-counted, so multiple loggers can target the same file of the same type (File to File, and SQLFile to SQLFile)
• Destination URLs are now mapped to the log type once opened.
• Destination.FileHandling now allows for re-opening log files.
• label is always used, after re-reading docs and code
• Error metadata is handled in a similar way to swift-log's StreamLogHandler.
• Added metadataProvider to the logger constructor

Full Changelog: 1.0.0...2.0.0