Support has_one to be compatible with 0.8.x
Includes links inside of linked resources

According to
http://jsonapi.org/format/#document-structure-resource-objects,

> Resource objects have the same internal structure, regardless of
> whether they represent primary or linked resources.

And then
http://jsonapi.org/format/#document-structure-resource-object-attributes,

> There are four reserved keys in resource objects:
>
> "id"
> "type"
> "href"
> "links"

This commits includes `links` inside of linked resources.
Merge pull request #727 from rails-api/include-links-in-linked-resources

Includes links inside of linked resources
Use type as key for linked resources

If type is `author` but the association is called `writer`, the linked
resource key should be called `authors`, e.g

    {
      ...
      linked: {
        authors: [{
          ...
        }]
      }
      ...
    }
Merge pull request #703 from ggordon/specify_serializer_from_controller

Support serializer and each_serializer options in renderer
Use the new beta build env on Travis

also remove the custom bundle install line as Travis does that by default
Merge pull request #729 from joshk/patch-2

Use the new beta build env on Travis
Fixes rbx gems bundling on TravisCI

Fixes https://github.com/travis-ci/travis-ci/issues/2821
Merge pull request #728 from rails-api/linked-resources-use-type-as-key

Use type as key for linked resources
Rename attribute with :key (0.8.x compatibility)
Merge pull request #720 from ggordon/attribute_with_key

Rename attribute with :key (0.8.x compatibility)
Explicitly set serializer for associations

Document specifying serializer for assocaition
Allow overriding the adapter with render option

Make it easy to use multiple adapters in an app.

use "adapter: false" to not use ams

make a test override config.adapter
Merge pull request #718 from ggordon/adapter_override

Allow overriding the adapter with render option
Fixes nested has_many links in JSONAPI

When linked resource had has_many links, all of them would use the
association from the first resource, causing all of the items to build
`links` with the same associations.

This fixes it by iterating over the serializers, not just the
attributes array.
Merge pull request #730 from rails-api/fixes-nested-has-many-links

Fixes nested has_many links in JSONAPI
Don't automatically include ActionController::Serialization
Merge branch 'explicit_serializer' into experimental
merge