I don't like the idea of a password encryption-capable module needing
a third-party library, but I liked this module even less. It doesn't
support parallelism, it doesn't support other versions of Argon2, it
doesn't support other types of Argon2; one of those types, Argon2id,
is more suitable for password hashing than Argon2d is, ...

It is also rather difficult to write a benchmarking utility for,
because it is not in libathemecore like our new Digest API is.

Now that we have a proper binding to a library, update the included
PBKDF2 benchmarking utility to support Argon2 as well. Change the
default type from Argon2d to Argon2id. Add automatic optimal crypto
module parameter benchmarking to the utility, and fix a long-standing
memory corruption bug in it. Finally, elaborate a lot on the various
configuration options of Argon2 in the example configuration file.

While we're at it, tweak the time recommendations in the example
configuration file too.