std::locale::global is unsafe

[amirgon]

Tabulate code calls std::locale::global in several places.
std::locale::global is not thread-safe and makes tabulate unsafe to use inside a larger multithreaded application.
An application might change the locale at any time and conflict with tabulate calls to std::locale::global.
This is not a theoretical issue, I actually experienced application crashes until I removed all std::locale::global calls from tabulate.

I suggest removing all calls to std::locale::global and either pass locale directly to functions that accept locale as an argument, or use imbue to configure a stream to a locale.