wostream not supported by units library

[daniel.macumber@…]

Use of hard coded std::string in io.hpp (and other headers) of units library prevents printing units to wostream using <<.

[Steven Watanabe]

(In [53293]) Allow printing to wostream. Fixes #3089.

[daniel.macumber@…]

This patch worked but did not cover output of absolute types to wostream. In absolute.hpp we need to add something similar to:

template<class Y> std::wostream& operator<<(std::wostream& os,const absolute<Y>& aval) {

os << L"absolute " << aval.value();

return os;

}

[Steven Watanabe]

(In [53577]) Allow absolute to be printed to std::wostream. Fixes #3089