Use cmake, not make/msbuild, in compile scripts

Our documentation and test scripts configure using cmake and then use the native build system to compile. E.g. libmongoc's installation documentation has this for Unix:

$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF ..

$ make install 

And this for Windows:

$ cmake -G "Visual Studio 14 2015 Win64" -DCMAKE_INSTALL_PREFIX="C:\mongo-c-driver" ..

$ msbuild.exe /p:Configuration=RelWithDebInfo INSTALL.vcxproj 

Using cmake for the build instructions may simplify this a bit, changing both build instructions to:

cmake --build cmake-build --config RelWithDebInfo --target install 

In addition, if we take this approach we may be able to consolidate some of compile-unix.sh, compile-windows.sh, and compile-windows-mingw.bat.

Documenting this as the way to build may also prevent users from accidentally mixing release/debug runtimes in their application, as there have been several related bug reports: CXX-1961, CDRIVER-3558, CXX-1780

This ticket is associated with the compilation script update.