add structure-overview.md
add structure-entry-scripts.md
Grammar fix
Merge branch 'master' of github.com:yiisoft/yii2
Merge branch 'master' of github.com:yiisoft/yii2
Add structure-extensions.md to translate into Russian
updated doc [skip ci]
fixed console guide and docs of FixtureController
Minor text adjustments
Docs about testing
Rewritten testing introduction, added environment setup to README.md, removed empty pages that were not referenced
expanded db-migration doc
Update db-migrations.md

fix a typo.
Fixes #4800.
fix bugs of BlameableBehavior in console application. In console application, \yii\console\Application doesn't have `getUser()` method. Use BlameableBehavior in console application will cause an exception.
Fixes #4736
First pass of edits
structure-extensions.md is translated to Russian
Added more notes and a book reference to testing intro
Replaced Amazon link with ISBN