Add #126: Add setImage() for GroundOverlay
Add #127: Add setBounds() for GroundOverlay
Add #128: Add setOpacity() for GroundOverlay
Bug fix #129: The bearing option of GroundOverlay does not effect in iOS
Add #130: setBearing() for GroundOverlay
Bug fix: GroundOverlay #128 #126
Added groundOverlay.html
Add getOpacity() and getBearing() for GroundOverlay
Add setZIndex() and getZIndex() for GroundOverlay
Add setFadeIn() / getFadeIn() for TileOverlay
Update tileOverlay.html
Update demo code
Bug fix: The `opacity` variable is undefined.