Log filtering rules in config file. For `Trace`s, `Level`s, sublevels, etc.
Log normalise source path in terminal print
Log have #[cfg(feature="threaded")] for deferring write to background worker
Warning: I dunno how safe calling fork() in an async context is... Which is currently what we're doing. Make it return an actual future instead, and do no awaiting on the child. Set pipe to block for child, but not for parent, etc.
