- Deprecated `yii\base\BaseObject::className()` in favor of native PHP syntax `::class`, which does not trigger autoloading
- Deprecated XCache and Zend data cache support as caching backends
- Deprecated `yii\BaseYii::powered()` method
- Added `yii\base\InvalidArgumentException` and deprecated `yii\base\InvalidParamException`
- Added `yii\BaseYii::debug()` and deprecated `yii\BaseYii::trace()`