We have `gcry_kdf_derive` now. For modern password hashing, it's better to have new API. To avoid dependency to thread support, it's good to decouple thread things and kdf computation.
- `gcry_kdf_open`
- `gcry_kdf_ctl`
- `gcry_kdf_compute`
- `gcry_kdf_close`
Possibly, user code can be something like following.
Argon2 and Balloon will be implemented. Possibly, scrypt too.