Add documentation for API typedef functions

src/ol/tileloadfunction.js

@@ -2,6 +2,10 @@ goog.provide('ol.TileLoadFunctionType');
 
 
 /**
+ * A function that takes an {@link ol.ImageTile} for the image tile and a
+ * `{string}` for the src as arguments.
+ *
  * @typedef {function(ol.ImageTile, string)}
+ * @todo stability experimental
  */
 ol.TileLoadFunctionType;