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/isDataView.js

@@ -0,0 +1,14 @@
+import tagTester from './_tagTester.js';
+import isFunction from './isFunction.js';
+import isArrayBuffer from './isArrayBuffer.js';
+import { hasStringTagBug } from './_stringTagBug.js';
+
+var isDataView = tagTester('DataView');
+
+// In IE 10 - Edge 13, we need a different heuristic
+// to determine whether an object is a `DataView`.
+function ie10IsDataView(obj) {
+  return obj != null && isFunction(obj.getInt8) && isArrayBuffer(obj.buffer);
+}
+
+export default (hasStringTagBug ? ie10IsDataView : isDataView);