Separate Build/Test directories

[jleung51]

CMake can build its files in a separate directory - for example, if the CMakeLists.txt file is in the parent directory, then cmake .. will build the files in the current directory. This means the build/ file will no longer need to be cluttered with the temporary files.

The test/ directory should contain the tests as well as the CMakeLists.txt file to build the executables, while the build/ directory should be empty for the built executables (and temporary CMake files).