Merge 4a72f15b7a into 426f5688a4

README.md

 *Libraries that implement data structure or storage techniques.*
 
 * [CakePHP Collection](https://github.com/cakephp/collection) - A simple collections library.
+* [DeepClone](https://github.com/symfony/php-ext-deepclone) - A PHP extension to export serializable values as plain arrays and reconstruct them.
 * [Fractal](https://github.com/thephpleague/fractal) - A library for converting complex data structures to JSON output.
 * [JsonMapper](https://github.com/cweiske/jsonmapper) - A library that maps nested JSON structures onto PHP classes.
 * [JSON Machine](https://github.com/halaxa/json-machine) - Provides iteration over huge JSONs using simple `foreach`.