Standard statistics using Welford's algorithm

 Statistics::Welford provides standard statistics (mean value,
 variance, standard deviation, minimum and maximum value as well as
 the number of elements) using Welford's algorithm.
 .
 Welford's algorithm is much more resource efficient compared to the
 naïve algorithm implemented in e.g. Statistics::Basic::StdDev or
 Catmandu::Fix::stat_stddev. It especially does not need to load all
 values into RAM at the same time, i.e. does not require an array
 containing all values.
 .
 See also
 https://en.wikipedia.org/wiki/Variance/Algorithm#Online_algorithm