Initialize a predictable RNG

[dinosaure]

I think there is still a use where you want to initialize the RNG so that it produces a predictable output. Typically, before the API change, it was possible to initialize the RNG with Fortuna and a seed. I think that this type of usage is still valid and that the deprecation on Mirage_crypto_unix.initialize should be removed. WDYT?

[hannesm]

I'm not sure I understand the demand for a "predictable RNG", but you can always:

let () =
  let g = Mirage_crypto_rng.create ~seed:"private" (module Mirage_crypto_rng.Fortuna) in
  Mirage_crypto_rng.set_default_generator g

Now, with Mirage_crypto_rng_unix.initialize -- there was no predictability given, since that used CPU instructions & whirwhind & getrandom for an initial seed.

Be aware that the set_default_generator is a global mutable cell, thus any other library may set it. To really ensure using the predictable RNG you want to have, pass the g explicit to generate.