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
Fix popover in icon example
Merge pull request #988 from fredj/icon_example

IE10 compatibility: no tooltip on icon.html example
Add more api doc
Add links to Proj4js and CONTRIBUTING.md
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.
Rename ol.layer.LayerBase to ol.layer.Base
Rename ol.layer.LayerGroup to ol.layer.Group
Rename ol.source.ImageSource to ol.source.Image
Rename ol.layer.ImageLayer to ol.layer.Image
Rename ol.source.TileSource to ol.source.Tile
Merge pull request #993 from pagameba/deviceorientation-ios

Detect iOS compass heading
Rename ol.source.DebugTileSource to ol.source.TileDebug
Rename ol.source.ImageTileSource to ol.source.TileImage
Rename ol.source.TiledWMS to ol.source.TileWMS
Rename ol.layer.TileLayer to ol.layer.Tile
Rename ol.test.source.MockTileSource to ol.test.source.TileMock
Rename ol.source.VectorSource2 to ol.source.Vector2