Merge branch '2.3' into 2.6

* 2.3:
  Adding an example of how the other format for attaching transformers looks
  fixed typo thanks to @OskarStark
  adding use statement
  using the aliases entity manager service name
  Many tweaks thanks to review
  Completely re-reading the data transformers chapter:

Author: weaverryan

book/forms.rst

@@ -1141,6 +1141,8 @@ the choice is ultimately up to you.
 
         $form->get('dueDate')->setData(new \DateTime());
 
+.. _form-as-services:
+
 Defining your Forms as Services
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~