Modification for DTD conformance

- Added date elements in various references to be conform to the DTD,
  which permit to build the I-D with xml2rfc 2.3.11.

Note that building with xml2rfc 2.3.11 changes a lot of things in the txt
format.
Change port in example

- Following comment by Stewart Bryant, changed the port in the example
  from 6100 to 6084.
Merge pull request #176 from petithug/stewart-bryant

Change port in example
Merge pull request #175 from petithug/dtd-conform

Modification for DTD conformance