International conversion of string values to double (or int)

[hjmjohnson]

Thanks to @ihnorton for bringing this to our attention in #394:

---

std::stod is risky in a different way: it is locale-dependent, so international users could see strange results or failures (due to parsing . and , incorrectly). Unfortunately this is another place where C/C++ stdlib has no clearly-superior options from what I can tell:

• use https://en.cppreference.com/w/cpp/locale/setlocale globally
• use a stringstream and imbue: https://stackoverflow.com/questions/1333451/locale-independent-atof with std::locale::classic() instead of std::locale("C") downside is stringstream may be slower, but I'm not sure if that matters here.

---

#394 is still considered an incremental improvement, so it will be merged as is for now.