Static compilation of LUA - not every distribution uses the same library name, so it's safer this way.
Create new base DGSystem class

The goal is to use this base class to implement as much functionality
as possible with only one code base for all operating systems. Due to
the planned Android and iOS ports this base class will be based on SDL2.
Initial SDL2 integration

Introduce SDL2 and - as an initial example - use it for thread delays.
Also introduce a _real_ FPS control while at it ;-)