#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.
Now I'm even more confused.  What is `base_flux`?  

In particular, how would someone know what the base_flux is supposed to be for their image?  What about the image is supposed to have a flux of 1e'/sec?  The average pixel?  It's way too low if that's what it is supposed to be.  Most images have more than that flux level just in the sky, never mind the objects with flux you care about.  (Well, from the ground anyway -- probably not for WFirst.)  

You refer to it as p'/T', but those letters don't mean anything to me either.  So I'm completely at a loss for how to interpret this.