Inspired by http://github.com/hashrocket/acts_as_featured/

ActsAsCompleted
==============
Allows ActiveRecord models to be specified as completed by updating a `completed_at` datetime (or timestamp) field on the model.

Also provides named scopes for completed and uncompleted finds.

Requires Rails > 2.1.0

Installation
============

Add a `completed_at` datetime field to any model that you want to be completed.

Example
=======

	# Add the column
	./script/generate migration AddCompletedAtToTask completed_at:datetime
	rake db:migrate

	class Task < ActiveRecord::Base
	  acts_as_completed
	end

	Task.completed
	# SELECT * FROM tasks WHERE tasks.completed_at IS NOT NULL

	Task.uncompleted
	# SELECT * FROM tasks WHERE tasks.completedd_at IS NULL

	@task.complete!
	# UPDATE tasks SET completed_at = '2008-07-08 15:58:34' WHERE id = 1

	@task.uncomplete!
	# UPDATE tasks SET completed_at = NULL WHERE id = 1

	@task.completed?
	# Return true if the task is completed, false if not