Add new guide upload-file

1.  UploadedFile::getInstances($model, 'file'); sees only one file if not set ```'file[]'```

```php
<?= $form->field($model, 'file[]')->fileInput(['multiple' => '']) ?>
```

2. ```$form->errorSummary(..)``` not return all errors of file attribute, but only the last.
So I had to invent.

```php
if ($model->hasErrors()) {
    echo '<pre>';
    print_r($model->getErrors());
    echo '</pre>';
}
```

So it should be?
MS SQL Server fix for older versions than 2012 (alternative solution)

This alternative solution LIMIT, OFFSET problem SQL Server version older than 2012.
fix error

fix error when if fields whose names are reserved word
Update QueryBuilder.php

fix error occurs when you use multiple databases.
fix #3478

it correct work with integer keys of list
Update QueryBuilder.php

solution used **heukirne** for the names of columns.
Masked input widget upgrade fixing #3196

Support contribution credits updated
Escaping of the special characters at 'MATCH' statement reworked
Merge branch 'master' of github.com:yiisoft/yii2
Merge pull request #3703 from kartik-v/patch-5

Masked input widget upgrade fixing #3196
Docs for Sphinx extension updated
Merge branch 'master' of github.com:yiisoft/yii2
Docs for Sphinx extension updated
Extra tab symbol removed
Typo fixed
Docs about handling missing translations added
yii\redis\ActiveRecord::deleteAll() refactoring - no need to write to socket 2 times when nothing found
yii\redis\ActiveRecord::deleteAll() refactoring - no need to write to socket 2 times when nothing found
Started Russian translation of the guide and internals
yii\redis\ActiveRecord::deleteAll() refactoring - code style updated