Starter code for the Duke project

todo, event, deadlineAdds a task to current list
Example of usage:
todo sleep, event wedding /at 2019-05-15, deadline submission /by 2019-04-22
Expected outcome:

listDisplay current list of tasks
Example of usage:
list
Expected outcome:

doneMark a task as completed
Example of usage:
done 1
Expected outcome:

deleteDelete a task from current list
Example of usage:
delete 3
Expected outcome:

findSearch for tasks with a keyword.
Example of usage:
find sleep
Expected outcome:

updateUpdate a task in the current list.
Example of usage:
update 2 description Mary's wedding, update 2 date 2019-06-07
Expected outcome:
