In case this becomes a module.

This spits out links in VimWiki syntax, which is more readable and useful
in context than just a raw list of grep results.

(For the grep results, I could always use `gf` to jump to the file, but
it didn't then get added to the VimWiki location list, so the back command
wouldn't work.)

This also uses an sqlite query against an already-built table instead of
pawing through a bunch of files on disk, which is probably faster.