Removed document_order() function, added internal_object() accessor and...

Removed document_order() function, added internal_object() accessor and exposed xml_node/xml_attribute constructor from internal object pointer (this makes implementing fast binding to scripting languages easier)

git-svn-id: http://pugixml.googlecode.com/svn/trunk@747 99668b35-9821-0410-8761-19e4c4f06640