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/proj/proj.js

@@ -100,6 +100,7 @@ ol.Projection = function(options) {
 
 
 /**
+ * Get the code for this projection, e.g. 'EPSG:4326'.
  * @return {string} Code.
  */
 ol.Projection.prototype.getCode = function() {
@@ -108,6 +109,7 @@ ol.Projection.prototype.getCode = function() {
 
 
 /**
+ * Get the validity extent for this projection.
  * @return {ol.Extent} Extent.
  */
 ol.Projection.prototype.getExtent = function() {
@@ -116,6 +118,11 @@ ol.Projection.prototype.getExtent = function() {
 
 
 /**
+ * Get the resolution of the point in degrees. For projections with degrees as
+ * the unit this will simply return the provided resolution. For other
+ * projections the point resolution is estimated by transforming the center
+ * pixel to EPSG:4326, measuring its width and height on the normal sphere,
+ * and taking the average of the width and height.
  * @param {number} resolution Resolution.
  * @param {ol.Coordinate} point Point.
  * @return {number} Point resolution.
@@ -124,6 +131,7 @@ ol.Projection.prototype.getPointResolution = goog.abstractMethod;
 
 
 /**
+ * Get the units of this projection.
  * @return {ol.ProjectionUnits} Units.
  */
 ol.Projection.prototype.getUnits = function() {
@@ -132,6 +140,7 @@ ol.Projection.prototype.getUnits = function() {
 
 
 /**
+ * Get the amount of meters per unit of this projection.
  * @return {number} Meters.
  */
 ol.Projection.prototype.getMetersPerUnit = function() {
@@ -140,6 +149,13 @@ ol.Projection.prototype.getMetersPerUnit = function() {
 
 
 /**
+ * Get the axis orientation of this projection.
+ * Example values are:
+ * enu - the default easting, northing, elevation.
+ * neu - northing, easting, up - useful for "lat/long" geographic coordinates,
+ *     or south orientated transverse mercator.
+ * wnu - westing, northing, up - some planetary coordinate systems have
+ *     "west positive" coordinate systems
  * @return {string} Axis orientation.
  */
 ol.Projection.prototype.getAxisOrientation = function() {
@@ -148,6 +164,7 @@ ol.Projection.prototype.getAxisOrientation = function() {
 
 
 /**
+ * Is this projection a global projection which spans the whole world?
  * @return {boolean} Wether the projection is global.
  */
 ol.Projection.prototype.isGlobal = function() {