Bind the public key cryptography, and then the random number generator

Dear gnutls guilers,

Here is the gnutls-random function that generates a random bytevector. Since the "random" name is already taken, I think it is a good idea to keep the "gnutls-" prefix.

What do you think?

PS: since the objective is to merge quickly, I took the liberty to rebase on top of !9 (merged) so that we avoid a cycle of CI/resolve conflicts/rebase.

Best regards,

Vivien