A very me-specific task grepper for vimwiki.

Saves some keystrokes on importing to wiki.

Uses git-diff-index.

Also adds `git ec` alias so maybe I remember to use this.

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.

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.

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

In practice this now includes diary entries.