doc: Add missing RFCs.

doc/mainpage.dox

@@ -184,6 +184,8 @@ It was later modified and expanded by the following RFCs.
     Authentication and Key Exchange for the Secure Shell (SSH) Protocol
  - <a href="http://tools.ietf.org/html/rfc4716" target="_blank">RFC 4716</a>,
     The Secure Shell (SSH) Public Key File Format
+ - <a href="http://tools.ietf.org/html/rfc5647" target="_blank">RFC 5647</a>,
+    AES Galois Counter Mode for the Secure Shell Transport Layer Protocol
  - <a href="http://tools.ietf.org/html/rfc5656" target="_blank">RFC 5656</a>,
     Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
 
@@ -203,6 +205,12 @@ do the same in libssh.
 
 @subsection main-rfc-extensions Secure Shell Extensions
 
+The libssh project has an extension to support Curve25519 which is also supported by
+the OpenSSH project.
+
+ - <a href="" target="_blank">curve25519-sha256@libssh.org</a>,
+   Curve25519-SHA256 for ECDH KEX
+
 The OpenSSH project has defined some extensions to the protocol. We support some of
 them like the statvfs calls in SFTP or the ssh-agent.