Xpath support for namespaces

Added basic support for namespace registration and resolution so that Xpath queries can effectively use namespaces that exist in the source XML files.

Added sentences for querying namespace usage:
*  the XML should use the namespace "(?P<namespace>[^"]*)"
*  the XML should not use the namespace "(?P<namespace>[^"]*)"

Also added country.xml to test basic namespace usage and updated the xml.feature to perform the functional tests.