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/csso/lib/replace/String.js

@@ -0,0 +1,12 @@
+module.exports = function(node) {
+    var value = node.value;
+
+    // remove escaped newlines, i.e.
+    // .a { content: "foo\
+    // bar"}
+    // ->
+    // .a { content: "foobar" }
+    value = value.replace(/\\(\r\n|\r|\n|\f)/g, '');
+
+    node.value = value;
+};