Refactoring LinkToHandler to easy overrides

Relax visibility of Linker and LinkToHandler methods.
Is necessary to create individual tests for Linker or the LinkToHandlerTest cover all?

https://github.com/caelum/vraptor-i18n/issues/28#issuecomment-49992192
With attribute I can @Specializes the Linker.
If you prefer a delegate method I change.