Please, add LOG4CL-EXTRAS

[svetlyak40wt]

This is a number of addons for LOG4CL. These addons allow:

• to do a context logging
• to log backtrace in case of unhandled error
• to log into JSON format suitable for uploading to Elastic Search

The repository is here: https://github.com/40ants/log4cl-extras

This system depends on 40ants-doc system: issue #2030