Update regarding Device Orientation Specification.

DeviceOrientation Event Specification (
http://w3c.github.io/deviceorientation/spec-source-orientation.html) has
been amended with the following changes:
- added 'deviceorientationabsolute' event,
- the already existing 'deviceorientation' event is now 'relative' by
default.

The idea is that 'deviceorientationabsolute' event can be used in Augmented
Reality applications (when the direction of the magnetic north is
important). While the 'deviceorientation' event would be suitable for
Virtual Reality applications or games.

In particular the reasons behind this change are the following:
- compatibility of 'deviceorientation' with Safari on iOS (where it is
'relative' by default).
- 'deviceorientation' does not require magnetometer anymore and is not
distorted by potential external magnetic field.
- usability of 'deviceorientation' for VR applications (e.g. no 'sensor
drift' which occurred in the previous 'absolute' implementation)

These changes have been implemented in Chrome for Android but are currently
in 'experimental' state, i.e. not yet enabled by default.

thanks,
Tim