Major QoI considerations:
- The facility is backported to C++14, same as libstdc++.
- Efforts have been made to minimize the header dependencies.
- The design is friendly to the uses of MSVC intrinsics (__emulu, _umul128, _BitScanForward, _BitScanForward64) but not implemented; future contributions are welcome.
Thanks to Milo Yip for contributing the implementation of __u64toa and __u32toa.
References:
https://wg21.link/p0067r5
https://wg21.link/p0682r1
We need to hide these names when _LIBCPP_STD_VER < 17, since we're not allowed to introduce new names into namespace std in older dialects.