Updated .gitignore for building on Mac OS X
Add support for CMake build system generator.

CMake can generate build scripts for a number of build systems,
including make, XCode, Visual Studio, and Eclipse.

In-source and out-of-source builds are allowed,
but the CMake people suggest out-of-source builds.

To do an out-of-source build using make:
mkdir build
cd build
cmake ..
make
make test

To do an out-of-source build using XCode:
mkdir xcode
cd xcode
cmake -G Xcode ..
Work on CMake
More CMake
Temporarily disabling unit tests on CMake