PN532 NFC/RFID reader implementation

[vytautassurvila]

Implementation via nfcpy. Solves #64

Sample configuration:

stream_modules:
  - name: nfc-scanner
    module: pn532
    device: ttyUSB0
    read_interval: 0.5

Note that streams does not support homeassistant discovery. One can workaround it with following homeassistant automation:

- alias: doorbell_mqqt_tag_scan_to_tag_scanned_event
  trigger:
    platform: mqtt
    topic: doorbell/stream/nfc-scanner
  action:
    event: tag_scanned
    event_data:
      tag_id: "{{ trigger.payload }}"