tag-reader: update to pi-rc522 2.1

This version of pi-rc522 gives us a wait_for_tag() method,
greatly reducing CPU usage.

requirements.txt

@@ -1,3 +1,7 @@
-pi-rc522==1.1.0
+appdirs==1.4.3
+packaging==16.8
+pi-rc522==2.1.0
+pyparsing==2.2.0
 RPi.GPIO==0.6.3
-SPI-Py==1.0
+six==1.10.0
+spidev==3.2

tag-reader.py

@@ -3,11 +3,21 @@ from pirc522 import RFID
 import RPi.GPIO as GPIO
 import sys
 
+import signal
+
 GPIO.setwarnings(False)
 
 rdr = RFID()
 
+def sigint_handler(signal, frame):
+  rdr.cleanup()
+  sys.exit(0)
+
+signal.signal(signal.SIGINT, sigint_handler)
+signal.signal(signal.SIGTERM, sigint_handler)
+
 while True:
+  rdr.wait_for_tag()
   (error, tag_type) = rdr.request()
   if not error:
     (error, uid) = rdr.anticoll()