- Use bash for `set -o pipefail`
- Fall back to simpler find command when the original command failed

Related: #1061

Instead of notifying the event coordinator (EventBox) whenever a new
line is arrived, start a background goroutine that periodically does the
task. Atomic.StoreInt32 is much cheaper than mutex synchronization
that happens during EventBox update.

Close #818

`TAGS=termbox make` (or `go build -tags termbox`)

Use hard-coded limit to keep it simple. An alternative is to dynamically
calculate the width of the visible area and use it as the limit, but it
can cause unwanted truncation of the query on screen resize/split.

Also extend default jump labels