metrics library has been added to CMakeLists.
metrics library is meant to support different metrics types: gauge, counter, histogram, reservoir, meter, timer, etc.
metrics: gauge metric type has been added.

Gauge is the simpliest metric type which sets value only.
Gauge has simple internal statistics (min/max values + corresponding timestamps, count).
Gauge keeps track of long double values.
metrics: counter metric type has been added.

Counter is simple metric which can be initialized with some value (by default it's 0), incremented and decremented.
Counter has simple internal statistics analogous to gauge's one (min/max values + timestamps, count).
Counter tracks unsigned long long values.
transaction has been added.

Transaction is meant to count running, blocked and paused times during some process.
separate libraries (metrics, transaction, etc.) have been replaced with common handy library.
handystats: previous versions of statistics & metrics have been removed
CMake: type of project library has been changed to static (was shared)
counter: value type has been changed to long long (was unsigned long long) as counter value could go below 0.
counter, gauge: clock type has been added.
events: event_message format has been added.
counter_events have been added.
gauge_events have been added.
transaction_events have been added.