Docblock improvements to the Config library and remove CI_Config::_assign_to_config()

Existance of _assign_to_config() is pointless as this method
consists just of a foreach calling CI_Config::set_item() and
is only called by CodeIgniter.php - moved that foreach() in
there instead.
diff --git a/system/core/Exceptions.php b/system/core/Exceptions.php
index c0caf2e..5562577 100644
--- a/system/core/Exceptions.php
+++ b/system/core/Exceptions.php
@@ -130,7 +130,7 @@
 	 * @param	string		$heading	Page heading
 	 * @param	string|string[]	$message	Error message
 	 * @param	string		$template	Template name
-	 * @param 	int		$statis_code	(default: 500)
+	 * @param 	int		$status_code	(default: 500)
 	 *
 	 * @return	string	Error page output
 	 */