Add a function named zetteldeft-upsert

[maw]

ref #94

@EFLS I started using this today. I bound it to C-c d u.

I wouldn't accept this as-is (if nothing else, the name doesn't fit with the general aesthetic you've laid out for zetteldeft commands) but I hope it can be the basis for something that is inclusionworthy.

For completeness' sake, I think there should be equivalent functions for zetteldeft-new-file-and-backlink and zetteldeft-new-file-and-link. It might be worthwhile to rework them all.

[EFLS]

I've just tried the zetteldeft-upsert function to better understand what it does, but get an error:

(wrong-type-argument stringp :preselect)

Any idea what I'm missing?

[maw]

I finally had a look at this. It turns out that :preselect and :initial-input are ivy-readisms.

3486781 fixes it, sort of. But the end result is far worse.

I think it could be improved by filtering the result of deft-find-all-files-no-prefix before passing them to the completing reader as options, although losing :preselect would still be unfortunate.

I'm sorry for taking so long to respond.

[maw]

@EFLS I've been using a personal branch for months which includes my completing read enhancements and this upsert functionality.

I can't remember for sure but I think what I did was create the upsert code in my personal branch which already included my completing read changes. Then I cherry-picked it back into a branch dedicated to upsert -- but I made mistakes, which you bumped into in #95 (comment).

I think it'll be easier to clean this up over once #91 lands.