Inherit custom headers

[f-mer]

This PR resolves #255 by making custom_headers inherit from ancestors.

I think this should be the expected behaviour but sadly is not backwards compatible. Should be backwards compatible.
Would love to hear some feedback 😃

class ArticleResource < JsonApiClient::Resource
end

class ApplicationController
  around_action :configure_json_api_client

  def index
    # will request articles with the authorization header set
     articles = ArticleResource.all
  end

  private

  def configure_json_api_client
    JsonApiClient::Resource.with_headers(authorization: 'Bearer TOKEN') { yield }
  end
end

[jsmestad]

100% yes!

[webandtech]

@chingor13 looks good to me and I don't see any backward compatibility issues. I am going to try to get my team more involved in helping this project. Let me know if I can help on the PRs.

[jsmestad]

For @f-mer and whomever else gets caught by this. I've pulled this into a released fork of this gem jsonapi-consumer along with some other outstanding bug fixes.

[mltsy]

I don't think this actually resolves #255 or its related issue #215 (maybe it resolves a different issue? See my comment on #255)