RoleAuthz - Simple role-based authorization
===========================================

Roles
------

    class Application < Merb::Controller
      role :name do |operator, target|
        # return true or false, depending on
        # whether or not this operator/target 
        # combination can have this role
      end
      # Examples:
      role :admin do |operator, target|
        operator.respond_to?(:admin) && operator.admin
      end
      role :owner do |operator, target|
        target.respond_to?(:owner) && target.owner == operator
      end
      role :guest do |operator, target|
        operator.nil?
      end
    end

Permissions
-----------

#### For resources:

    class Posts < Application
      authorize Post do
        for_role(:admin).allow(:all)
        for_role(:owner).allow(:all)
        for_role(:guest).allow(:index, :show)
      end
    end

#### For controllers:

    class NotAResourceController < Application
      authorize self do
        for_role(:guest).allow(:foo)
      end
      # foo is just an action
    end

#### Global:

    class Application < Merb::Controller
      # your role definitions
      authorize self do
        for_role(:admin).allow(:all)
      end
    end

Operators (user classes)
------------------------

Operator classes must call authorizable! somewhere. 

#### Example:
    class User
      include DataMapper::Resource
      authorizable!
  
      property :id, Serial
      property :login, String
    end

Operators may use the authorized? method to check authorization.

#### Examples:

    user = User.get(n)
    user.authorized?(:target => @post, :action => :edit)
    user.authorized?(:target => Posts, :action => :new)
    user.authorized?(:role => :admin)