This introduces a new command called "handshake" in the weechat relay protocol.
It should be sent by the client before the "init" command, to negotiate the way
to authenticate with a password.
3 new options are added:
* relay.network.auth_password
* relay.network.hash_iterations
* relay.network.nonce_size
The relay client is supposed to be safe by default, and the relay connection
should be protected by the different ways (restriction on IP address, SSL,
strong password, Time-based One-Time Password, local bind address and use of
SSH tunnel…).
So this option lets the user add extra security by allowing only some
commands (whitelist), or allowing any commands except a list of given
commands (blacklist).