Change nlmfield_field_widget_text_to_xml to use DOMDocument for XML generation

function nlmfield_field_widget_text_to_xml should use DOMDocument to generate the XML as it becomes easier to do empty checks on subfields. If a subfield within the text widget is left empty, then it should not be included in the XML.

http://drupalcode.org/project/nlmfield.git/blob/refs/heads/7.x-1.x:/nlmf...