[relax-ng] New spec draft

I've updated the spec:

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

I made the following changes:

- Section 4.20: <define> elements made unreachable by <notAllowed>
processing are removed

- Section 6: modify the first two paragraphs to deal with not()

- Section 7.1: use ref rather than element in the prohibited paths

- Section 7.3: add note that restriction on attribute wildcards is necessary
for closure under negation

James