This replaces the existing updateItems() + extension hook in favour of consistency with the register_dataobject() interface.
Note that this will likely be superseded by something to do with the Config API in the future.
Misc upgrade of module code so that site map.xml provides a index site map file based on the standards. Moved configuration vars to the Config API.
Considering how large a change this is, I've branched a 1.0 release off in github.
APICHANGE: moved GoogleSiteMapDecorator to GoogleSitemapSiteTreeDecorator to use the original for a hook for extending on googlesitemaps on dataobjects only.