random prime number generator for BigInt BigUint

[allan-simon]

I was wondering if this crate was the place for :

• support of is_prime etc. for BigInt and BigUint from the num crate using miller-rabin
• a weak but working random prime BigUint generator based on the is_prime above

of course i'm not asking that out of the blue :) the fact is i'm trying to reimplement in rust , a client-side skype library in rust , and the original code generates public / private key of 512 bits using this very simple algorithm

def random_prime(low, high):
    r = random.randint(low, high)

    if r%2 == 0:
        r+=1

    while True:
        if miller_rabin(r) == True:
            break
        r+=2

    return r 

so getting something similar for rust, would be of a great help , and as it's somethin i think not specific to skype, i was thinking it was a good idea to put it in an external crate