Support updating the badge via control sequence like iterm2

[kohnish]

iTerm2 supports updating the badge with printf like this. It's useful for updating in an environment like ssh and tmux.

#!/bin/sh
badge_str=$1
printf "\033Ptmux;\033\033]1337;SetBadgeFormat=%s\a\033\\"   $(echo -n "$badge_str" | base64)