sensor HAL major revision

mainly update the documentation, add new sensor types
and add a batch mode.

- TYPE_PEDOMETER, defines a pedometer sensor
- TYPE_SIGNIFICANT_MOTION, defines a sensor that triggers an
  event when the device is moving "enough". This sensor must allow
  the SoC to go into suspend, while it is enabled.
- TYPE_STEP_COUNTER, defines a pedometer but returns a step count
  (and looses precise timestamps, per step).

Change-Id: I3e20ff165851b7cb318f3c6637a6580de156b8fe