top-level website xml-site updated to use apache-forrest-0.6

I have updated the website instructions and configuration
files to use the latest Apache Forrest release (0.6)
to build the top-level documents.
http://xml.apache.org/guidelines.html#website

Sub-projects still continue to do their own thing.

The skin is still the same old tables-based skin
and not yet the modern CSS-based skin used at the
forrest.apache.org site. We can use that new one
if people so desire.

-- 
David Crossley