Define DOCURIUM when parsing

Define DOCURIUM to 1 when parsing the headers to let the source code
know it's being run for documentation parsing and give it a chance to
perform any workarounds they might need.

Author: carlosmn

lib/docurium/docparser.rb

@@ -26,7 +26,7 @@ def parse_file(orig_filename, files)
 
       # Override the path we want to filter by
       filename = File.join(tmpdir, orig_filename)
-      tu = Index.new.parse_translation_unit(filename, [], unsaved, {:detailed_preprocessing_record => 1})
+      tu = Index.new.parse_translation_unit(filename, ["-DDOCURIUM=1"], unsaved, {:detailed_preprocessing_record => 1})
 
       FileUtils.remove_entry(tmpdir)