Main points:

* Applies our documentation guidelines (names of files, punctuation in comments, etc.)

* AnimalsRecord was introduced before the primary abstract class. Before this
  point, stuff related to the primary database is explained first, and then you
  go for the extra database. This is the natural order, I think. I reordered
  for consistency.

* PrimaryApplicationRecord was missing connects_to.

* Fixes parent class for the example related to PrimaryApplicationRecord.