Adapt blinkraw utility to eye nonlinearity

I tried different RGB values and it always looked white to me and fading felt nonlinear. I implemented in the blink1raw utility a correction for the nonlinearity of the human eye:

corrected = 255 * (original_value / 255)^2.2

German source:

https://www.mikrocontroller.net/articles/Diskussion:LED-Fading#Diskussion_wissenschaftl.-technischer_Hintergrund