Code prettifying.
Wording and variable naming fixed.
User can now ask repository if it is available to create logger frontend with specific Sink and Formatter types.
Test added that checks frontend group registration.
Factories can now clean up themselves. Implemented frontend combination configuring.
Forgotten include added.
Shadowing unused variable.
It is now possible not to pay for unused sinks/formatters. Dropped unused mapping from logger severity to syslog.

Also some code reorganization done.
Logstash example has been repaired.