title: Enable indications with bluepy delegations
body: <p>I'm able to traverse the services and characteristics of my BLE device in bluepy, but I'm unable to get asynchronous indications to print.  I've looked at the suggestions in this <a href="https://stackoverflow.com/questions/32807781/ble-subscribe-to-notification-using-gatttool-or-bluepy">question</a>, but I can't get it working.</p>
  
  <p>It does work when using gattool:</p>
  
  <pre><code>$ sudo gatttool -b "DF:01:93:A9:86:FF" -t random  --char-write-req --handle=0x002c --value=0200 --listen
  Characteristic value was written successfully
  Indication   handle = 0x002b value: 00 8a 00 
  Indication   handle = 0x002b value: 00 8a 00 
  Indication   handle = 0x002b value: 30 30 2d
  </code></pre>
  
  <p>But I can't get bluepy to do the same:</p>
  
  <pre><code>from bluepy.btle import Scanner, DefaultDelegate, Peripheral, ADDR_TYPE_RANDOM
  
  class ReadCharacteristicDelegate(DefaultDelegate):
      def __init__(self):
          DefaultDelegate.__init__(self)
  
      def handleNotification(self, cHandle, data):
          print "  got data: 0x%x" % data
  
  periph = Peripheral('df:01:93:a9:86:ff', addrType=ADDR_TYPE_RANDOM)
  periph.setDelegate(ReadCharacteristicDelegate())
  periph.writeCharacteristic(0x002c, "\0x02\0x00")
  print "Enabled indications"
  while True:
      if periph.waitForNotifications(3.0):
          # handleNotification() was called
          continue
      print("Waiting")
  </code></pre>
  
  <p>It runs, but no indications ever print out:</p>
  
  <pre><code>$ sudo python simple.py 
  Enabled indications
  Waiting
  Waiting
  </code></pre>