Add deadlines to tasks

Is your feature request related to a problem? Please describe. I would like the ability to add deadlines to tasks, such as the ability to set a task to be completed by 01-30-19 Describe the solution you'd like a command something along the lines of tb --task complete modern algebra assignment 1 --due 01/30/2019 23:59 Additional context I think this with the subtasks feature request could make this both way more versatile and useful. I could probably find a way to integrate it with an existing calendar with these features (I've played around with the calendar API before)