Newsbeuter notifications.

.newsbeuter/config:
- notify-always no: notify only on new items.
- notify-program: use wrapper for notify-send.
- notify-format: %d new articles (%n unread articles, %f unread feeds)

newsbeuter-notifier.sh:
- Wraps notify-send for newsbeuter.

install.sh:
- Copy newsbeuter-notifier.sh to ~/bin.