Alpine Images with Argon2 support

[krenor]

#521
Would be awesome if it'd be pre-compiled for alpine images, too. 👍

[tianon]

The primary blocker here is that Alpine doesn't yet contain the necessary library in a released version:

• https://pkgs.alpinelinux.org/packages?name=*argon2*&branch=v3.7
• https://pkgs.alpinelinux.org/packages?name=*argon2*&branch=edge

[tianon]

(So there's not much we can do until that's resolved.)