Add attr_readers for all arguments
Give a better error when forgetting to implement authorised?

An interactor that is never authorised does not make
much sense. Which is not to say that it should be
possible to forget to define authorised?, just that
the user should get a more descriptive error when
she forgets.
Move methods around so that public stuff is first.
Always validate
Extract methods from initialize
No need for self here
Make sure we don't set instance vars in something that shouldn't have side-effects
update todo
Merge pull request #1 from marten/cleanup-operation

Cleanup operation