Fixed references in the guide
Merge pull request #2727 from Asetss/master

fix letter
Fixes #2734: `FileCache::keyPrefix` defaults to empty string now
Fixes #2735 

Adds DateTimeInterface support for Formatter
updated changelog
updated changelog
Merge pull request #2736 from ivokund/patch-1

Fixes #2735 - Formatter support for DateTimeInterface
Fixes #2737