Add Session.trackers and Session.sources

docs/api/session.md

 
 A reference to the [Time](time.md) utilities of this session.
 
+### gizmos
+
+`session.gizmos: Gizmos, read-only`
+
+A reference to the [Gizmos](gizmos.md) object.
+
 ### viewport
 
 `session.viewport: Viewport, read-only`
 
 A reference to the [Viewport](viewport.md) linked to this session.
 
-### gizmos
+### trackers
 
-`session.gizmos: Gizmos, read-only`
+`session.trackers: Iterable<Tracker>, read-only`
 
-A reference to the [Gizmos](gizmos.md) object.
+The [trackers](tracker.md) that are attached to the session.
+
+*Since:* 0.3.0
+
+### sources
+
+`session.sources: Iterable<Source>, read-only`
+
+The [sources of data](source.md) that are linked to the session.
+
+*Since:* 0.3.0
 
 ## Methods
 

src/core/session.ts

     }
 
     /**
+     * Visual cues for testing & debugging
+     */
+    get gizmos(): Gizmos
+    {
+        return this._gizmos;
+    }
+
+    /**
      * Rendering viewport
      */
     get viewport(): Viewport
     }
 
     /**
-     * Visual cues for testing & debugging
+     * Attached trackers
      */
-    get gizmos(): Gizmos
+    get trackers(): Iterable<Tracker>
     {
-        return this._gizmos;
+        return this._trackers[Symbol.iterator]();
+    }
+
+    /**
+     * Sources of data
+     */
+    get sources(): Iterable<Source>
+    {
+        return this._sources[Symbol.iterator]();
     }
 
     /**