[doc] Add origin_file_name attribute

Author: mpsonntag

odml/doc.py

@@ -37,6 +37,10 @@ def __init__(self, author=None, date=None, version=None, repository=None, oid=No
         self._date = None
         self.date = date
 
+        # Enable setting of the file name from whence this document came.
+        # It is for knowing while processing and will not be serialized to a file.
+        self._origin_file_name = None
+
     def __repr__(self):
         return "<Doc %s by %s (%d sections)>" % (self._version, self._author,
                                                  len(self._sections))