Added --border-width option to control added border around image.

[apnadkarni]

I wanted to be able to control the borders (hardcoded to 2 cells) added to the image so I added the --border-width option. The code ensures it is greater than 0 as setting it to 0 breaks the intersection code. There was a comment in the original code about border being hardcoded to 2 to work around some fill artifacts but I couldn't see which cases would cause this if set to 1.

I set version to include "borderwidth" in project.clj to distinguish my build. You probably do not want to pick that up.

Warning: I'm well versed in C and other languages but this is the first time I've touched Java code :-)