Make a "lazy" lens

[bmaddy]

It would be nice to only load certain attributes when they are requested. We might be able to do this by having each of our lenses return and operate on an enumerator instead of a value (we probably want to do this on the FedoraLens::Lens class). This way we could specify some model loads as being lazy like this:

# current way
attribute :related_item_title, [RDF::DC11.relation, Lenses.load_model(:some_class), RDF::DC11.title
# lazy way
attribute :related_item_title, [RDF::DC11.relation, Lenses.lazily, Lenses.load_model(:some_class), RDF::DC11.title

The related model would be loaded lazily when we call obj.related_item_title.