GCC compile error about confliting declaration of size_t.

- Happens when common/error.h is included from timer.cpp.
- No idea why I don't define size_t anywhere myself, don't want to waste any more time banging
  my head against this right now.
Added libformat (cppformat) dependency. cppformat has printf-like syntax with type safety.

- Added printing of sdl version compiled and linked against.
- Added FindCPPFormat module.