Adding build/ directory to .gitignore.

Adding CMake directory to make things buildable.
Updating CMakeLists.txt to depend on appropriate files.
Updating tutorial3.cu to reflect changes to CMakeLists.txt
Adding lib/ directory with additional files dependent on new CMakeLists.txt
Modified tutorial.cpp to reflect changes due to project being renamed gpuRayTracer.
Hardcoded tutorial number to 3, as that's the only one we should be using now, referencing another tutnum will fail.
Merge branch 'master' of http://github.com/navien21/GPURayTracer