Implement RSA benchmark-test

[GorogPeter]

In my code, I used commented asserts to specify the inputs. In my humble opinion, it (e.g. // assert(prime1 > 255);) looks better than a text one (e.g. // prime1 has to be greater than 255). Is it okay, or should I change it?

Moreover, in some cases, I preferred to use if and while statements that contain a short, single and simple instruction, without brackets. For me, it looks more readable and more straightforward than with them. Is it okay, or should I change it?

For example, this:

if (e == 0) return 1;
x = x % m;
if (e == 1) return x;
if (x <= 1) return x;

instead of this:

if (e == 0) {
    return 1;
}
x = x % m;
if (e == 1) {
    return x;
}
if (x <= 1) {
    return x;
}

[ksh8281]

Nice!
IMO style with benchmark is not important for us!

[zherczeg]

LGTM

[zherczeg]

This style is unusal, we should follow more common style.