Provide an interface for bulk-updating a Drawable

The renderer can now update any combination of a Drawable's position,
direction, scale, and effect values through a single function call. The
effect values will be adjusted according to per-effect conversion
functions to prepare the values for use inside the shader.

build/demo.html

@@ -23,9 +23,13 @@
     var scale = 100;
     function thinkStep() {
         direction += 0.1;
-        renderer.setDrawablePosition(drawableID, posX, posY);
-        renderer.setDrawableDirection(drawableID, direction);
-        renderer.setDrawableScale(drawableID, scale);
+
+        var props = {};
+        //props.position = [posX, posY];
+        props.direction = direction;
+        //props.scale = 100;
+
+        renderer.updateDrawableProperties(drawableID, props);
     }
     drawStep();
     setInterval(thinkStep, 1/60);