serializer_for Array
Tests for ActiveModel::Serializer.serializer_for for not array serializer
Merge pull request #610 from bolshakov/feature/array_serializer

ArraySerializer
* Rename NullAdapter to SimpleAdapter
* Introduce abstract Adapter class
* Organaze test structure to match convemtions
Add NullAdapater
* Configure adapter using ActiveModel::Serializer.config.adapter
* Get adapter instance using ActiveModel::Serializer::Adapter.adapter_for(serializer)
Serializer should be available wiithing adapter to inspect attributes and assotions
Test for SimpleAdapter#serializable_hash
Test for NullAdapter#serializable_hash
Concrete adapter should provide serializable hash for Adapter#to_json method
Move Adapter.adapter_for to Serializer.adapter
Add Serializer#associations
README: typo fix on attributes
Fix rails 4.0.x build
Dont allow failures on 4.0.x
Add .ruby-version to gitignore
Rails does not support const_defined? in development mode;
Use const_get instead, and rescue NameError
Merge pull request #614 from arthurnn/fix_build_40

Fix rails 4.0.x build.
Merge pull request #613 from spk/readme_fix_attributes

README: typo fix on attributes
Merge pull request #615 from tpitale/fix-serializer-lookup

Rails does not support const_defined? in development mode