Detect iOS compass heading

iOS webkit does not provide an absolute alpha, instead it provides
webkitCompassHeading.
Rename externs/html5.js to externs/closure-compiler.js

Add add a fix for issues:
  * https://code.google.com/p/closure-compiler/issues/detail?id=1084
  * https://code.google.com/p/closure-compiler/issues/detail?id=1088
Merge pull request #1 from fredj/deviceorientation-ios

Rename externs/html5.js to externs/closure-compiler.js
check iOS compass calibration via webkitCompassAccuracy

Ensure that webkitCompassAccuracy is not -1 as this indicates that the
compass has not been calibrated and its values cannot be trusted.
Merge pull request #993 from pagameba/deviceorientation-ios

Detect iOS compass heading
Add ol.DeviceMotion