Allow associations inline with contain specify their own finder methods

Sorry, pull #4413 was out of whack with the 3.0 base. This PR is up-to-date and a single squash of the changes needed for this.
Travis is complaining about allocating memory which is (should be) unrelated.

Refs issue #4408.

Thanks!
I will remove this last syntax option. It is not intuitive at all that it can be done and there are already too many