feat: RSA digital signature system

[MarcosNicolau]

Description
Implements RSA key generation, this process consists of:

1. Generating two random primes p,q.
2. Computing n as p*q.
3. Computing $\lambda(n)$ (Carmichael's totient function).
4. Compute d as the modular inverse of e in $\lambda(n)$.
5. Release n,e as the public key and d as the private key.

Considerations
To generate the two random prime numbers we do:

1. A factor test with the first 1000 prime numbers: this allows us to quickly discard non-prime numbers.
2. If (1) passes, we run a stronger primality test: Solovay–Strassen test.

With keys of large bits (up to 1024) the algorithm becomes too slow, it takes at lest around 100 seconds to run the Solovay–Strassen test without taking into account the time it takes to find a prime number first (this is more random and is not so deterministic). Via benchmarks (will be uploaded in a future pr) the bootleneck has been identified in the biguint division algorithm. Issue #30 with more details.

Finally, all the references used while writing this has been added to the docs.

Closes #28