src: establish context on PCSCLite constructor

- Remove SCardEstablishContext from get_card_readers.
- Initialize m_status_thread to NULL so calling PCSCLite destructor does not
  crash in case the thread has not been launched. For example when
  SCardEstablish context fails
- Thanks to Ludovic Rousseau for pointing that out @
  https://github.com/santigimeno/node-pcsclite/pull/15#issuecomment-56222251.
src: add error_msg to create pretty pcsc errors
src: fix for OSs not supporting PnP Notification

- Instead of waiting for the notification, it will poll every second for a new
  card reader.
- Thanks to Ludovic Rousseau for the help. See:
  https://github.com/santigimeno/node-pcsclite/issues/14
Version 0.3.3