Implement remote.plc poller performance monitoring
o Correct Python3 compatibility; no leading zeros on integers
o Pass new self.polling, failing, duration, counter and load
  attributes out from poller._poller thread to poller interface.
o Ensure that the _poller thread yields its Thread time quanta
  between polls, to prioritize any pending blocked writes.
o Make the simulted_modbus_plc robust on Python3, which differs
  in how it reports non-blocking before a subprocess.Popen comes up.
o Make remote_test.py's polls test robust, quicker.
o Advance to __version__ 1.9.1