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

首先检查链接的 Gist，并在 repository 中找到现有的资源过滤入口点。将当前单层嵌套资源的行为与所要求的更深层嵌套和 has_one 关系进行比较。当嵌套过滤器能够在多个包含层级上工作（包括 has_one 资源），并且项目测试覆盖该行为时，即视为完成。