random generator: consider using gnutls instead of ISAAC
GnuTLS _NONCE level might be suitable. TODO: profile.
- Advantages: smaller state (~2kB -> 140B), dropping extra code that we don't (want to) maintain in exchange for the lib that we depend on anyway, maybe better quality of randomness.
- Disadvantages: probably more CPU-intensive, but most likely not noticeable for our use cases.