Rename several conflicting constant names

- Had to add '_' to some constant names so that they would not interfer
  with record names

Change return type of SDL_GetTicks

- Change from SDL_stdinc_h to unsigned to simplify casting code in game
  loop

Add debug symbols

- Added command line -g for debugger symbols

Stubs Handle procedures and extend to game loop

adventure_loop.ads:
- Add specs for Handle_Input, Handle_Events, Handle_Integration
- Rename IsPaused to IsRunning

adventure_loop.adb:
- Move event handler code from game loop into Handle_Input procedure
- "Improve" game loop logic (it doesn't work!)
  - but it will.
    - one day...
- Game loop now:
  - Processes the deltas
  - Calculates interpolation
  - Yields thread control if necessary