normalize to unity

[Peter]

A new normalizer class that multiplies all values in the range with a value such that the sum of values is 1.0 afterwards.

[Peter]

This is very similar to Centralizer, but instead of subtracting a value from each element, each element is divided by a value. A copy-n-paste with replacing std::Minus with std::Divide would do it, but would prefer avoiding the the duplicated code, if possible.

[Peter]

In C++11 it's possible to have something like

template<typename T = statistics::Average>
using Centralizer = RangeNormalizer<std::minus<double>, T>;

In C++98 one seems to forced into inheritance

template<typename T = statistics::Average>
class Centralizer : public RangeNormalizer<std::minus<double>, T>
{};

and I'm hesitant whether that's a good idea.

[Peter]

In 3953:

refs #890. Implement RangeNormalizer?, a generalization of Centralizer and implement Centralizer as an alias of a specialization.

[Peter]

In 3957:

closes #890. Implement normalizer::UnityScaler?.