std.format add dash separators to large numbers

[Jouko Koski]

"bearophile" <bearophileHUGS at lycos.com> wrote:
> Andrej Mitrovic:
>> auto str = format("%s", 1000000);
>> assert(str == "1_000_000");
> I suggest to add such formatter/function to Phobos.

While 1_000_000 may be the right thing in program code, the outside world 
would probably like to have numbers printed out according to their locale 
conventions. This is even more important with floating point or monetary 
values.

So before just adding some formatter to Phobos, I think that such 
formatter's use cases should be considered quite carefully.

-- 
Jouko