Add initial CMake build system

[hughbe]

Work on #134

How to use (Windows)

cmake -G "Ninja" -DCMAKE_TOOLCHAIN_FILE=C:/Users/hughb/Documents/GitHub/vcpkg/scripts/buildsystems/vcpkg.cmake
ninja

How to use (Linux/macos)

cmake -G "Ninja"
ninja

This has almost identical behaviour to the make build system right now

Details

• The target guetzli builds guetzli.exe
• The target guetzli_static builds guetzli_static.lib
• The target butteraugli builds butteraugli.lib
• View is to remove and replace the existing make/visual studio build system when you guys give the go ahead