Method "yii\helpers\base\FileHelper::removeDirectory()" has been added.
Method "yii\helpers\base\FileHelper::findFiles()" has been added.
Method "yii\helpers\base\FileHelper::mkdir()" has been added.
"self" replaced by "static" at "yii\helpers\base\FileHelper::mkdir()".
Doc comments at "yii\helpers\base\FileHelper::findFiles()" have been recomposed using markdown format.
"filter" callback option has been added to "yii\helpers\base\FileHelper::findFiles()".
"yii\helpers\StringHelper" usage has been added to "yii\helpers\base\FileHelper".
"StringHelper::basename()" has been replaced by plain "basename" at "FileHelper".
Merge pull request #523 from klimov-paul/file-helper

FileHelper port from 1.1.x