Fix infinite recursion

The method for testing whether to include an association was causing
an infinite loop when two models referenced each other.
Merge pull request #722 from ggordon/stack_level_too_deep

Fix infinite recursion
Bugfix: include nested has_many association

Currently, doing `include: author.bio` would work correctly, but not for
has_many associations such as `include: author.roles`. This fixes it.

The problem was basically that we were not handling arrays for has_many linked,
as happens for ArraySerializers.
Merge pull request #726 from rails-api/json-api-include-with-nested-has-many

Bugfix: include nested has_many associations
Allow overriding the adapter with render option

Make it easy to use multiple adapters in an app.

use "adapter: false" to not use ams