set the VPN SAFI codepoint to (TBD) as it may not be 128
-convert some FIXME comments as XML comments
-change BGP-ID len to 4
-change IPv4, IPv6 ans ISO IDs to be followed by a PSN octet
-add some wording on pseudonode byte
-clarified some use of TLV and subTLV section
-reworded the TLV/subTLV ordering paragraph