Issue #1500268 by heyrocker: Add CHANGELOG entry for configuration system.

core/CHANGELOG.txt

 
 Drupal 8.0, xxxx-xx-xx (development version)
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+- Configuration:
+    * Added a centralized file-based configuration system.
+    * Allows module authors to provide configuration in a standard format.
+    * Implements functionality to get, set, add and remove configuration.
 - Included the HTML5 Shiv library to support HTML5 elements in IE 8 and below.
 - Included the following Symfony2 components:
     * ClassLoader - PSR-0-compatible autoload routines.