I made the decision to make this verify-only for three reasons:

1) This algorithm has been superceded by Argon2, which we have an
   encryption-capable implementation of already.

2) The module requires a third-party library, which may not always
   be available, and also may rely on platform architecture.

3) Earlier versions of this software do not support this library, so
   making it encryption-capable would create a serious obstacle for
   downgrading to an earlier version of this software.

Also remove `doc/CRYPTO-LIBRARIES` because it is duplicating much of
what is already in `dist/atheme.conf.example`.