v0.2

Refactor code: Refactor code for adding of deadline/event

An empty task description can be added into the task list.

Making the code check if the task to be added has no description
will be able to ensure clean data storage.

Let's make the DeadlineCommand and EventCommand constructors throw
a BeefyException when an empty task description is passed into it.

v0.1

Refactor code: Refactor Mark/Unmark task function

Marking/unmarking tasks during initialization will cause output to be
printed.

Checking whether we are marking/unmarking task in initialization phase
before deciding on the need for output will solve the issue.

Let's create a Boolean variable isInitialize to check if the function is
called in the initialization stage.