Deprecate AsyncLoggingHandler?

[gregw]

The fix for #1386 has made the normal LoggingHandler asynchronous! Was this deliberate? If so, should the AsyncLoggingHandler be deprecated as it now no longer changes behaviour.

[garrettjonesgoogle]

Hmm I think I should actually switch the main one back to synchronous. I overlooked the separate asynchronous class which people can use. What I do think should be done though is to switch the example to suggest the asynchronous one because it will be more performant.

[garrettjonesgoogle]

I think this needs to be cleaned up before GA.

[garrettjonesgoogle]

We should delete this altogether, and support a setting for sync v async in the logging config.

[michaelbausor]

Closed in #1716

[gregw]

Could the AsyncLoggingHandler be left as a deprecated extension of LoggingHandler, as that will make transitioning usage easier?