Nested included resources filters

This issue is a (choose one):

• Problem/bug report.
• Feature request.
• Request for support. Note: Please try to avoid submitting issues for support requests. Use Gitter instead.

Checklist before submitting:

• I've searched for an existing issue.
• I've asked my question on Gitter and have not received a satisfactory answer.
• I've included a complete bug report template. This step helps us and allows us to see the bug without trying to reproduce the problem from your description. It helps you because you will frequently detect if it's a problem specific to your project.
• The feature I'm asking for is compliant with the JSON:API spec.

Description

Hi guys, I'm sorry about how this issue is looking, don't have time to make it better.
Currently, (checked on 0.9.5, and it's probably the same on 0.9.7) filtering on nested resources works only for 1 level deep inclusion, i.e. included_resource.filter_key. I made some monkey-patches in my app, to make it work with nested resources inclusion, i.e. included_resource.another_included_resource.filter_key.
Also, I did some changes to make filters work with has_one relationships.

The code can be a little bit messy, but it's working, at least for my project. No blame, please :)

The code is here: https://gist.github.com/RoM4iK/1ce4eab45ed0ceafa8728ed487ccddbb

Inizia esaminando il Gist collegato e individuando il punto di ingresso esistente per il filtraggio delle risorse nel repository. Confronta il comportamento attuale delle risorse annidate a un solo livello con l’annidamento più profondo richiesto e le relazioni has_one. Il lavoro è completato quando i filtri annidati funzionano a più livelli di inclusione, comprese le risorse has_one, e i test del progetto coprono questo comportamento.