[rfa/doc] Add version to XML target descriptions

[Eli Zaretskii]

> Date: Tue, 12 Jun 2007 08:37:31 -0400
> From: Daniel Jacobowitz <drow@false.org>
> 
> Eli, does the documentation update look OK?

Yes, but I suggest to give "version" a @code markup here:

> +useful for XML validation tools.  The version attribute for
                                         ^^^^^^^