Add Argon2d and Argon2id support

Add Argon2d and Argon2id support

This is mostly about supporting Argon2id, because it is mandated by the
RFC, and sometimes recommended by people who know more than I do about
the threat models around passwords.

Argon2d is included as well because supporting it is practically free
(one character change and one constant).

Speaking of constants, I'm not sure whether the three `CRYPTO_ARGON2_*`
constants should be pre-processor definitions like they are now, or
proper `const uint32_t` declarations.

Link #243