This is yet another program that adjust a laptop screen backlighting.
This works only for intel_backlight compatible settings. This probably
should've already worked with xbacklight but apparently, in my case, it
doesn't.
This particular solution directly writes to the intel_backlight/brightness
file. Note that there is a udev rule to set this file as the video group, and
then we have a setgid binary as video group.
This sets the backlight as a percentage of maximum brightness.