Reverse engineer design from code

I am using the Sauerbraten (a.k.a. Cube Engine 2) game engine as the enabling technology for a project. This engine is free and open source (google for Sauerbraten). This project is currently blocked by lack of documentation and a code base that isn't too pretty to say the least. Your task will be to analyse the source code of the engine, and to a lesser extent the game examples, and produce design documents and developer documentation. The purpose of the documentation will be to provide developers with the information required to get a running start developing games with and modifying the engine. Happy bidding.