[benchmark] Report quantiles from samples
The default benchmark result reports statistics of a normal distribution — mean and standard deviation. Unfortunately the samples from our benchmarks are *not normally distributed*. To get a better picture of the underlying probability distribution, this adds support for reporting quantiles.
See https://en.wikipedia.org/wiki/Quantile
This gives better subsample of the measurements in the summary, without need to resort to the use of a full verbose mode, which might be unnecessarily slow.
