Add descending retrievability

[dae]

A partial fix for #3460. Some notes:

• This only adds the extra option for now, and does not change the default yet.
• The 'day', 'deck then day' and 'day then deck' orders sort by day primarily because it was the most efficient in older versions of Anki, and that is no longer as much of a concern. When making the this new sort order the default in the future, we may want to drop 'day' and 'day then deck', and replace 'deck then day' with 'deck then most retrievable first'.
• In the end, I decided not to add the special treatment of the current day for now, as I'd like to see how the simpler approach is received first.

What do you all think?

[user1823]

Looks good enough to me.

Just to note, this seems to remove the Relative Overdueness option for SM-2 users.

[abdnh]

LGTM

[abdnh]

Just to note, this seems to remove the Relative Overdueness option for SM-2 users.

It's synonymous with ascending retrievability - the new order also works with SM-2.

[user1823]

Sorry, I didn't look closely at the code.

[user1823]

This is fine. But, for a more accurate sorting (adding 0.001 to avoid division by zero introduces slight inaccuracy), we can calculate the reciprocal and then sort in the opposite direction.

So, it would become something like cast(due-{today} as real) / ivl {order}

[dae]

No objections to a more accurate implementation, but I'm nervous to change working code so close to a release - perhaps this could be fixed in a follow-up.