Task due dates

[joereynolds]

We need a way to signify a task's due date.
Currently a created task is completely open ended

I'm thinking we do the following:

Adding

jn todo --add "Do the dishes" --due '2035-03-03'

Adds a due date to the task do the dishes.

See #93 for possible solutions on how it would look

Filtering/Searching

Questions

• Can we think of a better way of encoding this information? It seems quite verbose