Add support for meta key

Test for meta_key serialization
Remove unneeded method aliasing of attribute reader: object, with the underscored class name of serializer, to fix issue where a model's attribute name matches that of the underscored prefix of the serializer
Fix failing tests on Rails master
move gemfiles/Gemfile.edge to root
no need to allow failures
Merge pull request #162 from frodsan/fix_edge_tests

Fix failing tests on Rails master
use proper tags for jruby on travis
add ruby-head to travis.yml
Merge pull request #163 from frodsan/yapr_travis

Yet Another PR on Travis
Update documentation to use ActiveSupport.on_load to disable root
Merge pull request #166 from gabetax/initializer-documentation

Update documentation to use ActiveSupport.on_load to disable root
Fix default_serializer_options, closes #112 & #113

Allow options such as :serializer, :scope, :root etc to be set via
default_serializer_options and allow the inline options to override such
defaults.
Merge pull request #114 from chancancode/fix_default_serializer_options

Fix default_serializer_options, closes #112 & #113
Merge pull request #138 from tchak/meta

Meta object
Take a stab at documenting AMS support.

Specifically when used in objects that are not ActiveRecord objects.
Test : use a deducted serializer on non-ActiveRecord models
use id methods
remove debugging code
Merge pull request #173 from jacortinas/document_ams_support_include

Document adding serializer support to normal Ruby classes and other ORM's.
Merge pull request #176 from hmsimple/id-methods

Use pluck(:id) or _id methods instead of associated objects