Differences to json-c

* we do NOT handle NUL characters inside strings or names
  At the time of fork, json-c did not properly handle this, but
  could at least, with tricks, generate outbound json with NUL
  in string values. We do not support this.
  This also means libfastjson is not 100% JSON compliant. Sorry
  for that, but we try to keep things working great in the C
  spirit, and that JSON feature simply doesn't play well here.
  If you need 100% JSON compliance, look for another library.
