Move completed tasks to Archive

[pslobo]

Building on the idea of #27 and a feature similar to what Taskpaper for macOS offers, it would be great to have an archive completed tasks that did the following:

1. Moves completed tasks to Archive with hotkey or command (this would ideally be a configurable Archive file);
2. Possibly append the completion or archive date to the task

For option 2, this isn't too different from what Slated: Move Task currently does. Here's a quick example:

Given the following structure

# Project A
- [ ] Task 1
- [x] Task 2

# Project B
- [x] Task 3
- [ ] Task 4

When moving a task with Slated: Move Task you'd get something like this

# Project A
- [ ] Task 1

My feature request would be that functionality be extended to Slated: Archive Completed which would render something like:

# Project A
- [x] Task 2 [archived 2021-06-07]

# Project B
- [x] Task 3 [archived 2021-06-09]

Reasoning I tend to keep a backlog file of tasks I need to complete on my projects. When I start the day, I look at the backlog and send any tasks I plan on working to the daily note.

I prefer to have leave the option Preserve incomplete tasks when moving enabled. That way, I know that a task was moved from daily note to daily note and can track the days I took to complete. Once complete, I mark it as done in the backlog.

The ability to archive completed tasks from that backlog to an archive file would be great to allow me a 30000 foot view of all that has been accomplished without the need of having to dig through all the daily notes.

Feel free to tell me this is a won't implement or if the idea isn't clear, I'll happily try and expand on it.