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/events/tests/prepend.js

@@ -0,0 +1,31 @@
+'use strict';
+
+var common = require('./common');
+var EventEmitter = require('../');
+var assert = require('assert');
+
+var myEE = new EventEmitter();
+var m = 0;
+// This one comes last.
+myEE.on('foo', common.mustCall(function () {
+  assert.strictEqual(m, 2);
+}));
+
+// This one comes second.
+myEE.prependListener('foo', common.mustCall(function () {
+  assert.strictEqual(m++, 1);
+}));
+
+// This one comes first.
+myEE.prependOnceListener('foo',
+                         common.mustCall(function () {
+                           assert.strictEqual(m++, 0);
+                         }));
+
+myEE.emit('foo');
+
+// Verify that the listener must be a function
+assert.throws(function () {
+  var ee = new EventEmitter();
+  ee.prependOnceListener('foo', null);
+}, 'TypeError: The "listener" argument must be of type Function. Received type object');