got retrieve_tasks_by_date to pass
added way to retrieve_completed_tasks_by_date with newest first
addded retrieve_incompleted_tasks_by_priority
added generic retrieval methods to get all completed or incompleted tasks
added tests for delete_task_by_id
implemented delete_task_by_id, passes tests
added assigning the associatied project id when a task is added to a project
refactored add_task to take a splat operator, passes all tests for single element adds
projects can add multiple tasks, passes tests
removed pending functionality to list all tasks created within Task class, don't see value
changed attr_accessor to some Task instance variables
added date sort to the incomplet_tasks_by_priority
implemented Task.reset_class_variables, learned from class