Adding gitignore that handles XCode project files
[engine][game] Added XCode projects.
Completed "Architect game/engine divide" task.
Completed "Architect engine (update/render) logic" task.
Added IGame game interface.
Added Chess game class.
Added Engine class to manage game and main update loop.
Added Sys class for system specific functions.
Added Sys_osx, osx specific implementations of the Sys functions.