Adopting C++17 features

[irrequietus]

Up to a point, things like C++17 folding expressions feature can be (partially) used for metaprogramming purposes in implementing catamorphisms, despite it was mainly designed for easing out features like... "concepts". Currently clause has adopted by default C++14. With compiler evolution into the newer standard this and features like that will be adopted while offering where possible the usual recursive instantiation alternative for previous standards. This is a very loose guideline so far and this issue is for tracking a series of changes that might occur while C++17 becomes better supported by compilers.