LetMe - authorization DSL

[stefanchrobot]

This looks great! I really like the idea of separating the rules from the implementation. Couple of notes:

• I’d prefer for the policy to be linked explicitly to the checks, something like use LetMe.Policy, checks: SomeModule (unless this is already the case?),
• I found this example a bit confusing:

@woylie

    action :read do
      desc "allows a user to read an article and to see a list of articles"
      allow true
      deny :banned
    end

I think it would read better as deny :banned?. Still, first it’s allow everything but then there are some “conflicting” rules. Would be great if it was obvious from the code (not the docs) how the rules are combined and what’s the behavior when no rules are specified (is it sum or intersection, allow by default or deny by default?). Maybe rename action macro to something else?