Hello Guix,

Attached is a patch to add the password hashing library Argon2.  It is a
dependency for opendht.

The source tree contains the directory "blake2".  At first I thought
this is a bundled version of blake2, but it seems that this is a
seperate implementation.  The sources bundled with Argon2 are
significantly different from the ones at
https://github.com/BLAKE2/BLAKE2.
My conclusion is that this is a Blake2 implementation made by and for
Argon2.  Thus I did not unbundle it.  Do you agree with this?

Thank you!
Best,
Lukas