- ensure HTML version is acutally HTML formatted
- added valid text version

fixes #6814
original issue #6748

docs/guide/tutorial-performance-tuning.md better wordings[ci skip]

docs/guide-ja/tutorial-performance-tuning.md - added [ci skip]

* 'master' of github.com:yiisoft/yii2:
  Update test-fixtures.md
  docs/guide-ja/tutorial-mailing.md - added [ci skip]
  docs/guide/tutorial-mailing.md - corrections [ci skip]
  docs/guide/tutorial-i18n.md revised [ci skip]
  Fixed typo
  docs/guide-ja updated [ci skip]
  docs/guide-ja/tutorial-i18n.md - completed [ci skip]
  docs/guide-ja/tutorial-i18n.md - WIP
  docs/guide-ja/tutorial-i18n.md - WIP [ci skip]
  docs/guide-ja/tutorial-i18n.md - WIP [ci skip]
  Update start-hello.md
  yii\db\ActiveQuery phpDoc fix

docs/guide-ja/tutorial-mailing.md - added [ci skip]

docs/guide/tutorial-mailing.md - corrections [ci skip]

this is needed to ensure search works immediately after the insert.

docs/guide/tutorial-i18n.md revised [ci skip]

Update start-hello.md

Docs guide ja tutorial i18n [ci skip]

fix typo

yii\db\ActiveQuery phpDoc fix 2

allows using logger without a Yii application now.

close #6739

close #6779

* 'master' of github.com:yiisoft/yii2: (23 commits)
  datepicker should show empty field when value is empty string
  complete docs about Nav to include the style
  Update tutorial-mailing.md
  Reverted #3665 (reverted from commit 2aa39499)
  Unit test for `yii\console\controllers\AssetController` advanced
  Doc comments for `yii\console\controllers\AssetController` extended
  `yii\console\controllers\AssetController` now handles bundle files from external resources properly
  skip requirements checker test on HHVM
  Update README.md in guide-es [skip ci]
  Add helper-array.md in guide-es [skip ci]
  a note about database naming style
  Add syntax highlighting [skip ci]
  docs/guide-ja/tutorial-core-validators.md - completed [ci skip]
  docs/guide-ja/tutorial-core-validators.md - WIP [ci skip]
  docs/guide-ja/tutorial-core-validators.md - WIP [ci skip]
  Fixed `\yii\authclient\OAuth2::refreshAccessToken()` does not save fetched token
  `\yii\authclient\AuthAction::defaultCancelUrl()` changed to use `yii\web\User::loginUrl`
  MongoDB PHP extension min version raised up to 1.5.0
  Были различные ссылки в русском гайде - привел все к английскому виду ссылки. Файлы по этим ссылкам еще не существуют поэтому переименовывать их и не нужно.
  Fixed typo.
  ...

close #6432
issue #2053

fixes #6471

Remove Content-Transfer-Encoding from the list of default download headers

without a `nav-tabs` or `nav-pills` class a nav is not complete.

http://getbootstrap.com/components/#nav

fixes #6768

Update tutorial-mailing.md