o Add missed <stdio.h>;

o conditionalize sdl_set_x11_parent on ifdef UNIX.
Include <stdio.h> when DIGGER_DEBUG is set.
Add missed <math.h> and <stdio.h>.
Include <stdio.h> when DIGGER_DEBUG is defined.
Fix sound on Windows/SDL.
Fix cross-compile on MinGW.
There is no "win_xxx.h" headers in this package, so that don't
try to unclude them.
GC lot of unused defines and conditionals for old platforms:

o _WINDOWS
o __WIN32__
o WIN16
o GNU32
o FLATFILE
o DIRECTX
o RUNTIMEDYNAMICLINK

This makes code much more clean and maintenable. Please note that
it does not mean Windows is unsupported now, quite on contrary,
SDL 2.0 version for Windows works great and we will be publishing
some pre-built binaries for that platform.