docs: def remove_label(self, to_remove):
          """
          Remove a label from the document. (-> rewrite the label file)
          """
          if to_remove not in self.labels:
              return
          labels = self.labels
          labels.remove(to_remove)
          with self.fs.open(self.fs.join(self.path, self.LABEL_FILE), 'w') \
                  as file_desc:
              for label in labels:
                  file_desc.write("%s,%s\n" % (label.name,
                                               label.get_color_str()))