agenda should only include unfinished tasks

[ingorichter]

Agenda is helpful to show what's next on your todo list. Unfortunately, tasks that are already done are included in the list.

It would be great to have agenda only show unfinished tasks. I don't think there is any value in looking at already finished tasks on the agenda.

Any thoughts on this?

[NonerKao]

It makes sense to remove completed todos in agenda mode and my patch is ready. What do you think about this, @gammons ?

[gammons]

@NonerKao that makes sense. I added a small comment but otherwise it works. Please add a test as well!