Changed gamma correction according to CIE LAB

[Benik3]

This method is more linear for eye then simple exponential curve mainly on low values.
Nicely described e.g. here: https://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/ More info about CIE Lab https://en.wikipedia.org/wiki/CIELAB_color_space

Also it looks like NeoEase::Gamma was used only here, but I leaved it in the code.

[Makuna]

NeoEase::Gamma is meant to be the same thing just as the formula. There are some animation tricks it can be used for; but it should match the gamma correction.

[Benik3]

I got it. Fixed, if you are still interested :)

[Makuna]

Finally got around to integrating these changes. Exposed them as a different gamma equation https://github.com/Makuna/NeoPixelBus/pull/651 GammaCieLab