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/partition.js

@@ -0,0 +1,9 @@
+var _group = require('./_group.js');
+
+// Split a collection into two arrays: one whose elements all pass the given
+// truth test, and one whose elements all do not pass the truth test.
+var partition = _group(function(result, value, pass) {
+  result[pass ? 0 : 1].push(value);
+}, true);
+
+module.exports = partition;