Add support for Argon2id Variant

[josephlr]

The upstream implementation added a third variant of Argon2 called Argon2id. This mode provides a middle ground between the Argon2i and Argon2d modes. It provides most of the side-channel resistance of Argon2i with most of the GPU resistance of Argon2d.

For consistency with upstream this variant should be added. I might have some time this weekend to put together a PR. It shouldn't involve much; the only crypto change is in how data-dependent addressing works. It looks like that's done here.

The rest would just be adding all the additional functions, tests, and documentation.