UTF-8 case folding in C++14

utf8.cc

#include <codecvt>
#include <iomanip>
#include <iostream>
#include <locale>
#include <string>

#include "zip.h"  // See https://gist.github.com/mortehu/373069390c75b02f98b655e3f7dbef9a

const auto low = u8"abcæøåαβγ";
const auto upp = u8"ABCÆØÅΑΒΓ";

int main(int argc, char** argv) {
  const std::locale locale("en_US.UTF-8");
  std::wstring_convert<std::codecvt_utf8<wchar_t>, wchar_t> ucs2conv;

  auto low_ucs = ucs2conv.from_bytes(low);
  auto upp_ucs = ucs2conv.from_bytes(upp);

  for (auto&& g : zip(low_ucs, upp_ucs))
  {
    std::cerr << std::setw(3) << std::tolower(std::get<0>(g), locale) << ' '
              << std::tolower(std::get<1>(g), locale) << '\n';
  }
}