- the HAVE_XXX flags could produce a name clash with some autoconf'ed
  software/library we will be using in production code. Rename to
  WOLF_SYS_HAVE_XXX or similar
- feedback to the c99 snprintf guy, errors like:
  - -1 instead of buffer size on boffer overflow
  - extern errno in mutli-threaded code
- add a lot more tests
- %zd and similar pointers: make format macros like PRIdPTR which
  get mapped to %ld. But what if snprintf could do a %zd and
  fprintf not?