Don't wrap array items in root element
serialize_ids call methods on the corresponding serializer if defined
Merge pull request #313 from geigerzaehler/fix_root

Don't wrap array items in root element
Add CHANGELOG.md entries
Add CONTRIBUTING.md
Always set a serializer for each item of an Array

model.active_model_serializer could return nil so we need to ensure that
if serializer is not setted we set DefaultSerializer to it.

This reverts commit 64ed05c484dc0add53183579a347b13d138ee944.

Fixes #318
Add campfire notifications
Turn off Travis' email notifications
Implements json_api singular resources
Implements json_api's collection resources
Implements json_api's client-ids meta info