Use safe_yaml gem & eliminate symbolized keys and values in yaml files.
Isolate and abstract YAML file loading into Kitchen::Config.

This commit introduces Kitchen::Loader::YAML which is responible for
reading and parsing .kitchen.yml and .kitchen.local.yml files to return
merged Hash data via the #read message. An instance of
Kitchen::Loader::YAML is created by default in Kitchen::Config unless
you want to inject your own instance in Config's constructor.

This class also adds the ability to disable ERB rendering if appropriate
and the ability to disable processing a .kitchen.local.yml file even if
it exists. It is also now possible to write your own custom loader class
that could read configuration out of JSON files, a DSL, a database, etc.

The constructor signature for Kitchen::Config has changed which may
break any external codebases that use Kitchen as a library. This was
done to allow custom loader objects and the ability to set configuration
options at object construction time (previously only attr_writer methods
were available for some tunables).
Create Kitchen::StateFile to read from & write to instance state files.
Merge pull request #58 from opscode/yaml-serialization

YAML Serialization