Allow specifying default sort method in config file

[strk]

I know I want list command to have --sort due --no-reverse by default, but haven't found a way to specify this in config file at this moment.

I guess GH-384 would give me an option but I'm wondering if it's cleaner to have something that works when you just run todoman list, maybe an option like default_list_sort_options ?

[WhyNotHugo]

default_command = "list --sort due --no-reverse" should work.

[WhyNotHugo]

default_sort would be a reasonable addition in any case.