Add CanvasSource.canvas

docs/api/canvas-source.md

 
 **Returns**
 
-A new source of data.
+A new source of data.
+
+## Properties
+
+### canvas
+
+`source.canvas: HTMLCanvasElement, read-only`
+
+The underlying `<canvas>` element.
+
+*Since:* 0.4.4

src/sources/canvas-source.ts

     }
 
     /**
+     * The underlying <canvas> element
+     */
+    get canvas(): HTMLCanvasElement
+    {
+        return this._canvas;
+    }
+
+    /**
      * A type-identifier of the source of data
      * @internal
      */