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/matcher.js

@@ -0,0 +1,13 @@
+var extendOwn = require('./extendOwn.js');
+var isMatch = require('./isMatch.js');
+
+// Returns a predicate for checking whether an object has a given set of
+// `key:value` pairs.
+function matcher(attrs) {
+  attrs = extendOwn({}, attrs);
+  return function(obj) {
+    return isMatch(obj, attrs);
+  };
+}
+
+module.exports = matcher;