YAML Serialization

The goal here is to isolate any serializing/deserializing of YAML files and abstract those actions to first order classes. This should help if any future auditing of YAML is required.

Currently this pull requests adds the [safe_yaml gem](https://github.com/dtao/safe_yaml) as a dependency to reduce the chances of arbitrary code injection and marshalling of Ruby objects by way of YAML files.

For more details, please read the commit messages in each commit.