Previously, libraries were loaded by instance_eval'ing them against
the same execution context used for control files. All resources were
registered against a single global registry when the `name` dsl method
was invoked. To obtain seperation of resources, we would mutate the
instance variable holding the globale registry and then change it back
at the end.
Now, we instance_eval library files inside an anonymous class. This
class has its own version of `Inspec.resource` that returns another
class with the resource DSL method and the profile-specific resource
registry.
