document aspect ratio enum

src/common/enums/aspect-ratio.enum.js

@@ -1,10 +1,11 @@
 var AspectRatio = Object.freeze({
-  Initial: -1,
-  Reset: 0,
-  Automatic: 1,
-  FitWidth: 2,
-  FitHeight: 3,
-  Fixed: 4,
+  Initial: -1,    // page default
+  Reset: 0,       // reset to initial
+  Automatic: 1,   // set by Aard
+  FitWidth: 2,    // legacy/dynamic: fit to width
+  FitHeight: 3,   // legacy/dynamic: fit to height
+  Fixed: 4,       // pre-determined aspect ratio
+  Manual: 5,      // ratio achieved by zooming in/zooming out
 });
 
 export default AspectRatio;