It seems that CMake 3.0.0's GUI sets the toolset to `vc120_xp` by
default, and it can't then be overridden in a CMakeLists.txt. Generating
using the command line is therefore more reliable.
Removed zlib dependency. Boost is now found by CMake. Each library now has separate root directory variables for greater flexibility. A few variables have been renamed for clarity/standardisation.