[ ] Add a config file
[ ] Use a better filter than a simple median, maybe a kalman filter
[x] Add a way to customise the brightness curve
	Percieved brightness is not linear, on low light you need a slightly higher
	brightness and on high light you can get away with a lower brightness
	than the max, the goal is to find the right curve for the screen
[ ] Automatically detect backlight device, or at least make it configurable
[ ] Add signal handlers
	[ ] SIGUSR1 to reset the user offset
	[x] Handle kill by closing all file descriptors
	    (every read is done by only keeping the file open for as long as it is needed)
	[ ] Handle suspend and resume, usually suspending means that the screen is
	    turned off so do not apply user offset
[ ] Account for DPMS and do not apply offset in that case