incremental_statistics: boost::accumulators removed.
config: configuration replaced with config in include, source files and configuration functions.
metrics: gauge counstructor with initial value removed.
incremental_statistics: clear() method added that clears all statistics data (config parameters stay the same).
metrics: counter counstructor with initial value removed.
metrics: counter init() method added that clears previous state and initializes counter with specified value.
config: configuration mechanics reworked.
incremental_statistics: incremental statistics configuration opts can be passed to the constructor now.
internal: added missing header.
metrics: timer and incremental statistics configuration opts can be passed to the timer constructor.
metrics: incremental statistics configuration opts can be passed to the gauge constructor.
metrics: incremental statistics configuration opts can be passed to the counter constructor.