docs: def _get_corenlp_version():
      "Return the corenlp version pointed at by CORENLP_HOME, or None"
      corenlp_home = os.environ.get("CORENLP_HOME")
      if corenlp_home:
          for fn in os.listdir(corenlp_home):
              m = re.match("stanford-corenlp-([\d.]+)-models.jar", fn)
              if m:
                  return m.group(1)