[relax-ng] Compact Syntax conformance

The conformance section of the Compact Syntax spec still remains to be
written.

It's not hard to describe conformance for a validator that supports the
compact syntax.

What is not clear to me is whether we also need to describe conformance for
a translator from the compact syntax to the XML syntax:

- if we don't, then the rules on translating annotations have no effect as
far as conformance is concerned; and these rules are quite important

- if we do, then the problem is this: the translation in the spec doesn't
produce very pretty output; trang expends a fair amount of effort to pretty
things up, by, for example, using a name attribute rather than name child
element or by using prefixes rather than ns attributes; this shouldn't be
disallowed but on the other hand I don't think the spec should get into this
sort of cosmetic issue

James