[UK][Guide] typos
 [ci skip]
Private method 'CFileHelper::mkdir()' has been converted into public 'CFileHelper::createDirectory()'.
CHANGELOG has been updated.
Doc comments at 'CFileHelper::createDirectory()' has been fixed.
CErrorHandler has been refactored to respect errorAction on AJAX request.
Issue #2753 has been added to CHANGELOG
CErrorHandler::errorAction via AJAX has been added to UPGRADE
Unnecessary comment at CErrorHandler::render() has been removed.
Merge pull request #2830 from klimov-paul/2753-error-action-with-ajax

Fix #2753 CErrorHandler::errorAction ignored at PHP error + AJAX request
CDbCommand::buildQuery() no longer throw exception if 'from' is missing.
Issue #2654 has been added to CHANGELOG
Merge pull request #2834 from klimov-paul/2654-db-command-optional-from

Fixes #2654: Allow CDbCommand to compose queries without 'from' clause
Merge branch 'master' of https://github.com/yiisoft/yii into uk_docs
[UK][Guide] typos
 [ci skip]
Merge pull request #2835 from yiiframework-com-ua/uk_docs

[UK][Guide] typos
Merge pull request #2827 from klimov-paul/enh-file-helper-create-directory

Enhancement: CFileHelper::createDirectory