PRICE - image filtering and manipulation Code

handle edges by holding off last pixel value

filter up to the borders by mirroring the image

update interface

one single pass to treat borders, instead of several loops. Slighly slower, but more uniform and readable code

cast parameter

round to third decimal to compensate rounding errors while inc/dec stepper

provdide extern definition to be C99 compliant for clang

filter colr images and filter alpha channel

add stepper and improve controller

do not use intermediate image, also just pad image by keeping the last value