added color comparison functions and expanded "difficult" defn

Added:
- function that calculates CIEDE 2000 color difference
- function that calculates average color of contour and determines how
many deviant pixels there are
- openMP to speed the summation of pixels
- beginnings of a programmatic definition of a “difficult” contour to
match
Merge branch 'contourmatching-opencv' of https://github.com/izewiske/3Hat into contourmatching-opencv