Build 10052011 Released 10th May 2011. Includes source code of the first build.
This is the source code which you can use under the license of GPLv3. This is nowhere near complete, but I thought I'd might as well share my current progress.
This build is very limited since it's the first one, but making maps and adding more levels works fine. Just mess around with 1.map.
Please read README, LICENSE and INSTALL.