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.

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

In practice this now includes diary entries.

Just a quick index of logs, for the moment.