code: def history_file(self, location=None):
          
          if location:
              # Hardcoded location passed from the config file.
              if os.path.exists(location):
                  return location
              else:
                  logger.warn("The specified history file %s doesn't exist",
                              location)
          filenames = []
          for base in ['CHANGES', 'HISTORY', 'CHANGELOG']:
              filenames.append(base)
              for extension in ['rst', 'txt', 'markdown']:
                  filenames.append('.'.join([base, extension]))
          history = self.filefind(filenames)
          if history:
              return history
docs: Return history file location.