pbarker@bluebottle:~/rc/pymavlink(pr/more-pymavlink-fields)$ ./mavlink_bitmask_decoder.py heartbeat base_mode 65533
  MAV_MODE_FLAG_CUSTOM_MODE_ENABLED
! MAV_MODE_FLAG_TEST_ENABLED
  MAV_MODE_FLAG_AUTO_ENABLED
  MAV_MODE_FLAG_GUIDED_ENABLED
  MAV_MODE_FLAG_STABILIZE_ENABLED
  MAV_MODE_FLAG_HIL_ENABLED
  MAV_MODE_FLAG_MANUAL_INPUT_ENABLED
  MAV_MODE_FLAG_SAFETY_ARMED
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
  [UNKNOWN]
pbarker@bluebottle:~/rc/pymavlink(pr/more-pymavlink-fields)$