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/lodash/_replaceHolders.js

@@ -0,0 +1,29 @@
+/** Used as the internal argument placeholder. */
+var PLACEHOLDER = '__lodash_placeholder__';
+
+/**
+ * Replaces all `placeholder` elements in `array` with an internal placeholder
+ * and returns an array of their indexes.
+ *
+ * @private
+ * @param {Array} array The array to modify.
+ * @param {*} placeholder The placeholder to replace.
+ * @returns {Array} Returns the new array of placeholder indexes.
+ */
+function replaceHolders(array, placeholder) {
+  var index = -1,
+      length = array.length,
+      resIndex = 0,
+      result = [];
+
+  while (++index < length) {
+    var value = array[index];
+    if (value === placeholder || value === PLACEHOLDER) {
+      array[index] = PLACEHOLDER;
+      result[resIndex++] = index;
+    }
+  }
+  return result;
+}
+
+module.exports = replaceHolders;