SASL support

The only supported methods are PLAIN and EXTERNAL, the latter is untested as of
now.
The code gets the values from the keys named sasl_{mechanism,username,password}
specified for each chatnet.

src/core/server-setup-rec.h

@@ -8,6 +8,9 @@ char *address;
 int port;
 char *password;
 
+int sasl_mechanism;
+char *sasl_password;
+
 char *ssl_cert;
 char *ssl_pkey;
 char *ssl_pass;