Could we have mod in std.math?

[bearophile]

Caligo:

> I'm hoping to see something like the above mod function in Phobos someday.

I'd like that, for both int/long/BigInts. And I'd like some functions for BigInts:
- divmod: returns both % and div and %, but it's more efficient if you need both values;
- gcd
- pow: with a third optional argument (like in Python pow built-in) to quickly compute (x ^^ y) % z.

Bye,
bearophile