incremental_statistics: internal stats from gauge have been moved out to separate class.
metrics: internal stats have been replaced with incremental_statistics (were gauges).
configuration: "gauge" section has been renamed to "incremental-statistics".
json_dump: output format of interval metrics' statistics has been changed.
configuration: handystats::config::defaults namespace with default configuration parameters has been added.
timer: now metrics::timer is multi-instance timer (it supports multiple simultaneously active instances).
internal_timer: internal_metrics::internal_timer is now just wrapper over metrics::timer (like internal_gauge and internal_counter).