[MEDIUM] add support for anonymous ACLs

[MEDIUM] add support for anonymous ACLs

Anonymous ACLs allow the declaration of rules which rely directly on
ACL expressions without passing via the declaration of an ACL. Example :

   With named ACLs :

        acl site_dead nbsrv(dynamic) lt 2
        acl site_dead nbsrv(static)  lt 2
        monitor fail  if site_dead

   With anonymous ACLs :

        monitor fail if { nbsrv(dynamic) lt 2 } || { nbsrv(static) lt 2 }