metrics: attribute moved from handystats::metrics to handystats namespace.
metrics_dump: common map of metrics splitted into two maps - metrics and attributes.
internal: 'handystats.internal.size' metric removed.
metrics_dump: metric object replaced with corresponding statistics object in metrics map.
json: metrics json writers removed.
chrono: fallback to "mfence; rdtsc;" call to get TSC value if rdtscp instruction is not supported.