* Added fraction accumulator
* Added binomial proportion interval computers: Wald, Wilson Score, Clopper Pearson, Jeffreys
* Width of intervals for all classes can be set via deviation or confidence_level
* Support valarray in histogram::fill
* Add fraction and count to user guide
Co-authored-by: Hans Dembinski <hans.dembinski@gmail.com>
Co-authored-by: Hans Dembinski <HDembinski@users.noreply.github.com>
* Bug-fix of weighted_sum: variance was not calculated correctly when normal histogram was added to weighted histogram with weighted_sum storage
* Several minor improvements to accumulator interfaces
* add weighted_mean::sum_of_weights_squared
* sum of default constructed mean and weighted_mean is now equal to default constructed object
* thread-safe returns a reference to self in operators just like the other accumulators
