Update demo to use Webpack

webpack.config.js

@@ -0,0 +1,10 @@
+const path = require('path');
+
+module.exports = {
+  entry: './demo/main.js',
+  output: {
+    path: path.resolve(__dirname, 'demo/dist'),
+    filename: 'bundle.js'
+  },
+  devtool: 'source-map'
+};