message: Add StepCount message attribute block
diff: @@ -310,6 +310,14 @@ the attributes will not be included.
  For instance, the FeatureCount attribute of a VibrateCmd message
  will refer to the number of vibration motors that can be controlled
  on a device advertising the VibrateCmd message.
  +* _StepCount_ (array of unsigned int): For each feature, lists the
  + number of discrete steps the feature can use. Returning to the
  + VibrateCmd example from the above _FeatureCount_ specification, if a
  + device had 2 motors, and each motor has 20 steps of vibration speeds
  + from 0%-100% (this is exactly what the Lovense Edge is), the
  + _StepCount_ attribute would be [20, 20]. Having the array allows use
  + to specify different amounts of steps for multiple vibrators on the
  + device.
  ---
  ## DeviceRemoved
  