Arrays 2.0.0

Major version of yiisoft/arrays was released:

• New ArrayHelper::group() that groups the array according to a specified key.
• Support for iterable objects in ArrayHelper::map() , ArrayHelper::index() , ArrayHelper::group() , ArrayHelper::htmlEncode() and ArrayHelper::htmlDecode .
• ArrayHelper and ArraySorter are now final.
• Fixed incorrect default value returned from ArrayHelper::getValue() when key does not exist and default is array.