[relax-ng] New DTD compatibility draft

I've done a new draft of RELAX NG DTD compatibility:

 http://www.thaiopensource.com/relaxng/compatibility.html

The changes are:

- Version bumped to 1.0

- Added a RELAX NG schema to Appendix A

- Added a paragraph to section 4 describing the infoset modification for
default attributes

- Slightly expanded the description of infoset modification in section 5 for
ID/IDREF (is this enough?)

Please review these changes, especially the schema, which is new and
non-trivial.

James