Now have a getCache method in Storage.
Added another cache test.
Added a clearCache method.
Save now takes a model type too.

It means you have to be more explicit but there is a lot more control.
Also, there would be a lot more hackery to get the save function to work
out the real constructor. This is the most simple, robust and efficient
way.
Added and tested saving models.
Save is now store. Makes more sense.

Save can be the method that commits the cache to localStorage for
example.