Primality certificates

[fjarri]

See https://en.wikipedia.org/wiki/Primality_certificate for an overview.

We could add:

• Pratt certificates. Simple, but the calculation can be slow.
• Atkin–Goldwasser–Kilian–Morain certificates. Requires some EC machinery; perhaps primeorder could be used for that.
• Pocklington certificates. Those can be used for random prime generation; although it is unclear if the generated primes are "random enough".