Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/underscore/modules/invert.js

@@ -0,0 +1,11 @@
+import keys from './keys.js';
+
+// Invert the keys and values of an object. The values must be serializable.
+export default function invert(obj) {
+  var result = {};
+  var _keys = keys(obj);
+  for (var i = 0, length = _keys.length; i < length; i++) {
+    result[obj[_keys[i]]] = _keys[i];
+  }
+  return result;
+}