Easy access control and roles for CRUD operations.

Easy Access provides a mixin for your User model that adds a simple role-based
access control system for the standard CRUD operations. A default access control
routine is supplied, but it can be overridden on a model-by-model basis allowing
for very fine-grained control.

Every CRUD operation has a corresponding User method and model hook. Implement
the model hooks(e.g. can_be_viewed_by?, can_be_edited_by?, etc.) and/or the
default AccessSystem::has_privilege_for? to customize your specific access
controls.