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/clean-css/lib/optimizer/level-2/properties/is-mergeable-shorthand.js

@@ -0,0 +1,11 @@
+var Marker = require('../../../tokenizer/marker');
+
+function isMergeableShorthand(shorthand) {
+  if (shorthand.name != 'font') {
+    return true;
+  }
+
+  return shorthand.value[0][1].indexOf(Marker.INTERNAL) == -1;
+}
+
+module.exports = isMergeableShorthand;