Updated Cart.php to handle quantity changes differently (now auto-increments), also updated the changelog to reflect this change for the people that are currently using this library
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 6f41f45..7110441 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -47,6 +47,7 @@
    -  CI_Loader::_ci_autoloader() is now a protected method.
    -  Modified valid_ip() to use PHP's filter_var() when possible (>= PHP 5.2) in the :doc:`Form Validation library <libraries/form_validation>`.
 	 -  Added custom filename to Email::attach() as $this->email->attach($filename, $disposition, $newname)
+   -  The Cart library now auto-increments quantity's instead of just resetting it, this is the default behaviour of large e-commerce sites.
 
 -  Core