chrono: tsc_clock performance improvements.
histogram: bin consists of center, volume and data timestamp.
math_utils: weighted_average and solve_quadratic helper functions added.
statistics: multiple config parameters replaced with config::statistics struct.
statistics: quantile and entropy dependency on moving_avg removed.
histogram: bin merge criteria changed to "distance between bins' centers".
benchmarks/load: print timer's quantiles.
chrono: get rid of std::chrono interface.
chrono: chrono::time_unit enum added (TICK, NSEC, USEC, MSEC, SEC, MIN, HOUR, DAY).
chrono: chrono::clock_type enum added (TSC, SYSTEM).
chrono: chrono::duration added (stores integer value and time_unit).
chrono: chrono::time_point added (stores duration and clock_type which represents epoch).
tests: check on interval statistics error weakened.