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/intersection.js

@@ -0,0 +1,19 @@
+import getLength from './_getLength.js';
+import contains from './contains.js';
+
+// Produce an array that contains every item shared between all the
+// passed-in arrays.
+export default function intersection(array) {
+  var result = [];
+  var argsLength = arguments.length;
+  for (var i = 0, length = getLength(array); i < length; i++) {
+    var item = array[i];
+    if (contains(result, item)) continue;
+    var j;
+    for (j = 1; j < argsLength; j++) {
+      if (!contains(arguments[j], item)) break;
+    }
+    if (j === argsLength) result.push(item);
+  }
+  return result;
+}