xeps: updated xep-0355 (namespace delegation): Several updates according to feedbacks: - Added attribute filtering, mainly to manage correctly MAM - Simplification of configuration in admin mode: no more <iq/> negociation - Delegations notifications to the managing entity are now done with a <message/> stanza - Forwarding now use XEP-0297 to avoid server to parse every stanza and a to have a cleaner separation - The behaviour when managing entity is unavailable is specified - Use of namespace in field var for client mode negociation is now mandatory - Behaviour when managing a delegation kept between session in client mode, when managing entity is not available, is specified - Implementation note added for in-order processing issue (thanks to Kurt Zeilenga for pointing this) - Added an note for discovery nesting with attribute filtering - Updated namespace to reflect incompatible changes

$ORIGIN <domain>.
$TTL 1D
@     IN SOA   <hostname> <hostname> (
                        <date>    ; serial
                        8H        ; refresh
                        4H        ; retry
                        4W        ; expire
                        1D )      ; minimum

                NS      <hostname>
www             CNAME   <hostname>
localhost       A       127.0.0.1
<hostname>      A       127.0.0.1

_xmpp-client._tcp.<domain>. 18000 IN SRV 0 5 <c2s_port> <hostname>.<domain>.
_xmpp-server._tcp.<domain>. 18000 IN SRV 0 5 5269       <hostname>.<domain>.