A CMakeLists.txt to replace the makefile

The game can be build out of source like this:

mkdir build
cd build
cmake ..
make

it has to be run out of the source directory so resource paths come out right:

./build/cataclysm

The list of source files has to be manually maintained, though there probably is a way to make it automatically add any source file in the list directory to be built.

I think it is easy to generate project files for Visual Studio or similar but I haven't tried it.