This involves changing grepprg, running, and then changing it back.

Not entirely optimal, but the location window has some good features.

Changes notes-links-for output to match (ish) grep format.

This is incredibly specific to my vimwiki setup at the moment.  It'll
probably expand to include other things, but I decided to just jam it into
one nice generic top-level namespace for now.

- changes various BPB_Foo functions to s:FOO, which is cleaner and does
    less trampling on the global namespace

  - adds some vimwiki log / link utilities based on an SQLite db I'm
    building elsewhere

  - comments slightly clearer about how unlikely this is to work for most
    users

  - removes some cruft, including an experimental scratch wiki