Add case to xml_find_template_parm for VECTOR_TYPE

I am getting the following errors when trying to parse classes that use Eigen:

xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type
xml_find_template_parm encountered unsupported type vector_type

Not sure this is the right fix, but it silences the messages :-)