Add postpone function

[varac]

I'd like to propose a postpone function so you can extend the due date from the cli easily:

    todo postpone 1w 123

(with 1w short for 1 week) i.e. or however time abbreviations are already implemented.

[WhyNotHugo]

My only nitpick is that I prefer todo postpone 123 1w, because this ordering sounds more intuitive, and because I'd like to always keep IDs first (for all commands).

Other than that, this sounds quite useful as an edition shortcut (though I'd like to avoid having too many).

[varac]

My only nitpick is that I prefer todo postpone 123 1w

+1

For lazy ppl like me a batch operation could be super helpful as well :D :

todo postpone --all --priority=high 1w