* Implemented left/right-concave border segments
* Fixed ConvexConcave border image
It was flipped horizontally.
* Implemented border left/right-concave detection
* Moved border images into their own directory
They're not really icons, after all.
* Cleaned up code a bit and added some more comments
* Applied requested change and consistified some function names
* Removed the old border images
I was sure I already did this, but apparently not.
