3D Euclidean Distance Transform for Variable Data Aspect Ratio

Added citation information as many people had requested.

Replaces bwdistsc with the earlier introduced experimental bwdistX, which uses forward-backward version of algorithm, improving speed up to 10x vs native bwdist

Adds experimental bwdistX for user testing, which uses forward-backward version of algorithm and is up to 10x faster than native bwdist

Included bwdistsc1 that allows restricting calculations out to a certain distance, which may accelerate calculations in some cases, see readme. Also contains a fix for Matlab version detection routine, thanks to Tudor Dima.

The code had been improved to better handle certain type of problems (cavities). It also contains fix allowing use of function with plain 2D images.