WIP: non-maximal suppression function (nonmaxsup)

Nonmaximal suppression is quite useful for edge detection.  This is a translation of a matlab function from http://www.csse.uwa.edu.au/~pk/research/matlabfns/Spatial/nonmaxsup.m (who has a number of other nice matlab functions available under a permissive license).

This function works for column-major images (and arrays), but needs some work to work for row-major arrays.  It also needs to be split into two functions, as one part of the functionality is to do subpixel localization of the peak, which might not always be wanted/needed.  (I find it believe it useful, e.g., for the hough transform, although I haven't verified this yet.)

I would love some tips on how to approach converting this to handle different image orientations.