Add extracted source directory and README navigation

extracted-source/node_modules/lodash-es/_setToArray.js

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+/**
+ * Converts `set` to an array of its values.
+ *
+ * @private
+ * @param {Object} set The set to convert.
+ * @returns {Array} Returns the values.
+ */
+function setToArray(set) {
+  var index = -1,
+      result = Array(set.size);
+
+  set.forEach(function(value) {
+    result[++index] = value;
+  });
+  return result;
+}
+
+export default setToArray;