BEGIN WORK ON ACTIVE CONTOURS

ADDED active countour stuff folder. mainly stuff downloaded from online.

functions  that I wrote:
sym_grad_map: remaps greyscale image so the average value of A where B
is selected (so hopefully the average value of PT) is the new maximum
value and things decrease linearly on either side. file also includes
stretch function which takes an image with a range less than the max and
stretches its values across the entire range.

vec2vol and vol2vec interconvert a 3d martrix to a 1d vector.