PARSEC: Password Authentication using Response Signed with Elliptic Curve

new authentication plugin that uses salted passwords,
key derivation, extensible password storage format,
and both server- and client-side scrambles.

It signs the response with ed25519, but it uses stock
unmodified ed25519 as provided by OpenSSL/WolfSSL/GnuTLS.

Edited by: Sergei Golubchik