logging: Write Logs for Machines, use JSON

Looks like a nice new challenge to use JSON also for debug / trace output.

I always found unstructured debug / trace output awful, and of course mine has been “key-value” for a long time.
I learned that “at home”, the Karlsruhe Ada Compiler construction team, back in the 80-s.

• Graylog Extended Log Format
• ruby, github: https://github.com/Graylog2/gelf-rb
• perl, METACPAN: Log::Log4perl::Layout::GELF
• perl, github: log4perl_gelf