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/without.js

@@ -0,0 +1,9 @@
+var restArguments = require('./restArguments.js');
+var difference = require('./difference.js');
+
+// Return a version of the array that does not contain the specified value(s).
+var without = restArguments(function(array, otherArrays) {
+  return difference(array, otherArrays);
+});
+
+module.exports = without;