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/cjs/isEmpty.js

@@ -0,0 +1,20 @@
+var isArray = require('./isArray.js');
+var keys = require('./keys.js');
+var _getLength = require('./_getLength.js');
+var isArguments = require('./isArguments.js');
+var isString = require('./isString.js');
+
+// Is a given array, string, or object empty?
+// An "empty" object has no enumerable own-properties.
+function isEmpty(obj) {
+  if (obj == null) return true;
+  // Skip the more expensive `toString`-based type checks if `obj` has no
+  // `.length`.
+  var length = _getLength(obj);
+  if (typeof length == 'number' && (
+    isArray(obj) || isString(obj) || isArguments(obj)
+  )) return length === 0;
+  return _getLength(keys(obj)) === 0;
+}
+
+module.exports = isEmpty;