Based on phasemoji.  Fails if no php.

Async here is great.

I was messing with this at... Some point in the last few years.

This just wraps the older calendar(1) invocation for the moment, just
adding a layer of indirection so it can include other data.

In case this becomes a module.

For querying overall page list.

This is modeled on ,. for inserting a link.

Uses metadata.db to find links targetting a particular page / tag, and
output in one of tsv, vimwiki list, vim location list, or fulltext.

Can be restricted to links from pages with dates, which makes it usable
for pulling logs.

Fully replaces the former:

  - notes-links-for, of which it's a superset

  - notes-logs-by-link

  - notes-logs-for which was used for fulltext of a log, and wrapped
    notes-links-for

This commit pulls into vim config as well.

This needs work.

...and print a helpful error message.

This adds a bunch of stuff I needed on a fresh Ubuntu install; I think
most of it should overlap fine with a stock Debian circa Bullseye.

I needed the exa out of cabal for the way I'm using exa, but it does exist
in the apt repos.

...rather than something which happens to be in log/.

In practice this now includes diary entries.

A example of manipulating header self-links and a table of contents.

This is mostly useless, but I didn't want to forget how I did it.