bwdist algorithm in Julia

For a project based on satellite data, it was necessary to use a bwdist alogirhtm which computes the Euclidean distance transform of a binary image and returns the nearest pixel as well.

However, since Julia is still quite a new, but powerful, language and bwdist a computationally expensive algorithm is, there was not such an implementation fully available.
Therefore, we helped in developing and optimizing a partially implemented algorithm which can now be used in Julia's offical Images.jl package.