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