Provide a combined grammar and grammar checker #15

This has been brought up in various proposal discussions (e.g. #2 (comment)) regarding compatibility of the proposals with the current XPath and XQuery grammars, and the various extensions (Full Text, Updating, Scripting).

At a minimum, this should provide an xpath and an xquery ebnf grammar file, and tools to verify that (as a separate project).

Should this also include full text (xpath and xquery variants), updating (xquery), and scripting (xquery) grammars?

Some options:

1. Reuse the tools used by the W3C WG to verify the grammar.
2. Use the parser that is used by the xquerydoc tool that generates an xquery parser in xquery from an ebnf.
3. Use some other parser generation tools (Java based?).