Uncomment ES6 module syntax

This removes the special comment part of the ES6 module syntax,
opting to enable ES6 module syntax by default.

It also appends `.js` to all import paths to better support in-browser
loading.

core/display.js

@@ -10,12 +10,11 @@
 /*jslint browser: true, white: false */
 /*global Util, Base64, changeCursor */
 
-/* [module]
- * import Util from "./util";
- * import Base64 from "./base64";
- */
+import Util from "./util.js";
+import Base64 from "./base64.js";
 
-/* [module] export default */ function Display(defaults) {
+
+export default function Display(defaults) {
     this._drawCtx = null;
     this._c_forceCanvas = false;