#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.
@chazshapiro - can you comment on Mike's question about the specificity of the IPC formula from Jason's writeup?
(I'm not sure if you're following this pull request, but if you aren't, you can click on the link in the e-mail to get to this comment, and Mike's is right above this one.)