code: def build_single_worker(queue, templates, base_output_dir):
      
      while True:
          scheme_file = queue.get()
          if scheme_file is None:
              break
          build_single(scheme_file, templates, base_output_dir)
          queue.task_done()
docs: Worker thread for picking up scheme files from $queue and building b16
      templates using $templates until it receives None.