add work-in-progress XML material file
add wrapper for xpath number query
add wrapper for xpath string query
add function element with attributes for testing
parse function XML element
adopt new XML layout
add interface class for attribute function
add proxy class for attribute function
add python class for attribute function
add call attribute to <code> element;
adopt python function
load python build environment
fix: add library_handle as argument to wrappers
implement xpath wrapper
add function query_number_of_arguments
fix: typo query_number_of_attributes
cosmetics
testing: disable protected
add function query_return_type
use namespace viennamaterials
migrate to xml_types representation