Added test cases for sprite priority algorithm.
Started restructuing project to move all non core source files out of
the core directory
Placed all file reading/writing routines into seperate modules
Moved SDL graphics routines  out of the graphics module and into its own self
contained file.
Moved framerate adjusting outside of graphics and into its own module.
All SDL related code is now in their own self contained area. Can
easily introduce a new framework with the core in the future
such as QT if needed.
Added a simple logger
Created debug module which now has debugging logic seperated from
the main module. Core is now mostly portable.