Add more content for the API doc

Involves additions to (there will be subsequent pull requests for other
classes):
- ol.Attribution
- ol.Collection
- ol.Expression
- ol.Feature
- ol.Geolocation
- ol.Map
- ol.Object
- ol.Overlay
- ol.Projection
- ol.View2D
- ol.control.Attribution
- ol.control.Control
- ol.control.FullScreen
- ol.control.Logo
- ol.control.MousePosition
- ol.control.ScaleLine
- ol.control.Zoom
- ol.control.ZoomSlider
- ol.dom.Input
- ol.filter.Filter
- ol.filter.Geometry
- ol.filter.Logical

src/ol/control/zoomslidercontrol.js

@@ -29,6 +29,14 @@ ol.control.ZOOMSLIDER_ANIMATION_DURATION = 200;
 
 
 /**
+ * A slider type of control for zooming.
+ *
+ * Example:
+ *
+ *     var zoomslider = new ol.control.ZoomSlider({
+ *       map: map
+ *     });
+ *
  * @constructor
  * @extends {ol.control.Control}
  * @param {ol.control.ZoomSliderOptions=} opt_options Zoom slider options.