Update return values
Update interface
Removed double cache prefix
Replace 'dynamic' keyword with 'mixed'

'dynamic' is not a valid keyword, see
http://phpdoc.org/docs/latest/guides/types.html#keywords
Merge pull request #5368 from barryvdh/phpdoc-fixes

[PHPDocs] Replace 'dynamic' keyword with 'mixed' + use FQN
Merging. conflicts.