internal_metrics: all internal metrics replaced with handystats::metrics
system_stats: all major components have stats namespace with its statistics
json_dump: json dump is constructed from metrics_dump map (+ dump timestamp)
metrics_dump: by now metrics_dump map doesn't contain dump timestamp
configuration: json_dump is controlled by metrics_dump ("to-json" boolean parameter)
configuration: sleeping on empty message queue parameter removed (by now thread sleeps for some small interval and consumes about 10% of single CPU even if there's nothing to do)