MongoDB Cache class added as draft.
Merge branch 'master' of github.com:yiisoft/yii2 into mongodb-cache
Unit test for MongoDB Cache advanced.
Update i18n.md

Correction name ru_RU zh_CN to ru-RU zh-CN
Merge pull request #1953 from djfly/patch-2

Update i18n.md
Re-added removed initialization of array
More specific description of language property of the application
Optimized code a bit
And optimized even more
Fixes #1845: removed pagination from debug panels.
minor fix of exception display.
Fixes #1897: Make gii diff markup copy paste friendly
Update core-code-style.md
Array short
Merge pull request #1961 from marsuboss/patch-2

Array short
Merge pull request #1960 from marsuboss/patch-1

Update core-code-style.md
Doc comments for MongoDB Cache fixed.
Merge pull request #1951 from klimov-paul/mongodb-cache

MongoDB Cache class
Doc comments for MongoDB Session updated.
Code style at redis readme fixed.