Get rid of stability annotations and document stability with api

This change adds a stability value to the api annotation, with
'experimental' as default value.

enum, typedef and event annotations are never exportable, but
api annotations are needed there to make them appear in the
docs.

Nested typedefs are no longer inlined recursively, because the
resulting tables get too wide with the current template.

src/ol/framestate.js

@@ -12,6 +12,11 @@ ol.PostRenderFunction;
 
 
 /**
+ * Function to perform manipulations before rendering. This function is called
+ * with the {@link ol.Map} as first and an optional {@link oli.FrameState} as
+ * second argument. Return `true` to keep this function for the next frame,
+ * `false` to remove it.
  * @typedef {function(ol.Map, ?oli.FrameState): boolean}
+ * @todo api
  */
 ol.PreRenderFunction;