Safe handling of primes/candidates

[fjarri]

In many applications of this library, like RSA or Paillier encryption, the primes being checked or generated are supposed to be secret. Can we enforce the zeroization of them throughout the library? This will have to be extended into crypto-bigint as well.

[ok-john]

Do you think it's better to zeroize on drop with macros or manually zeroize?