utility to set backlight intensity on a laptop

usage:

          bl [ +val[%] | -val[%] | val[%] ]
          
if no argument given, then current brightness level is printed

+val will increment brightness by that amount
-val will decrement brightness by that amount
val will set brightness to that amount

a percentage of maximum brightness can also be used by appending '%'

brightness control is exposed via /sys/class/backlight/intel_backlight
on my system. check your system and change if necessary.

brightness is enforced within the range 0..max_brightness