#552 Detector non-linearity and reciprocity failure

A basic method to apply any desired non-linearity on an Image has been included to begin with. The non-linearity can be specified by a LookupTable or as a function, possibly with parameters, that can act on NumPy arrays. In addition, it also includes a feature to correct for reciprocity failure. A basic unit test to test these functionalities have also been built.
>The first sentence, "Applies the given non-linearity function (NLfunc) to the image, and returns a new image of the same datatype." is, imo, completely sufficient. It just applies some function to each pixel in the image. It is up to the user to apply the right function at the right time.

I would be happy with that minimalist approach, here, if you guys are ( @arunkannawadi & @rmandelb ).