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/autoprefixer/lib/old-value.js

@@ -0,0 +1,22 @@
+let utils = require('./utils')
+
+class OldValue {
+  constructor(unprefixed, prefixed, string, regexp) {
+    this.unprefixed = unprefixed
+    this.prefixed = prefixed
+    this.string = string || prefixed
+    this.regexp = regexp || utils.regexp(prefixed)
+  }
+
+  /**
+   * Check, that value contain old value
+   */
+  check(value) {
+    if (value.includes(this.string)) {
+      return !!value.match(this.regexp)
+    }
+    return false
+  }
+}
+
+module.exports = OldValue