INSPEC Object: Add a 'ref' object

[aaronlippold]

We are at the point now were we really do need to add the 'ref' element to the InSpec Object. This will support the AWS benchmark work.

As it is now, the use of tag ref: is breaking/outside the DSL of InSpec and that just ins't good form. It will also force us to add extra and non-standard processing and interface to the standard json data structure and well in the end will just cause extra work that won't be stable moving forward.

Please add a quick PR to the InSpec object to add ref as an instance var.