cxxomfort: $title

cxxomfort rel.20210622

Simple backports for C++ - http://ryan.gulix.cl/fossil.cgi/cxxomfort/

Member cxxomfort::cxxostd::as_const (T &t) noexcept
Member cxxomfort::cxxostd::is_permutation (It1 ini1, It1 fin1, ItA iniA): Source: cppreference.com