A-Frame plugin: rename event to arstarted

docs/api/plugin-aframe.md

 
 ## Events
 
-### ar-started
+### arstarted
 
-The `ar-started` event is emitted when the main loop of the AR scene is set up, just after the AR session starts.
+This event is emitted on the scene when the main loop of the AR scene is set up, just after the AR session starts.
+
+*Since:* 0.4.2. Previously, this event was called *ar-started*.
 
 **Details**
 

plugins/aframe-with-encantar.js

         scene.setAttribute('renderer', { alpha: true });
 
         // pause the scene until we're ready
-        scene.addEventListener('ar-started', () => {
+        scene.addEventListener('arstarted', () => {
             scene.play();
         });
         scene.addEventListener('loaded', () => {
 
             // we're done!
             const scene = this.el;
-            scene.emit('ar-started', { ar: this });
+            scene.emit('arstarted', { ar: this });
+            scene.emit('ar-started', { ar: this }); // backwards compatibility with 0.3.0 - 0.4.1
             return session;
         })
         .catch(error => {