I manually made these changes because they
disabled some substantial amounts of code,
and I wanted to make sure this wasn't due to
original code having bugs or deviating from
the specification

switch from fopen to fopen_s on later MSVCs

Proper pointer check before deleting

minor warn correction

Explicit CDECL needed for qsort comparison function

QSORT only takes CDECL, but project settings can define different defaults for calling conventions.

gcc warning: unused parameter removed for macro STBTT_free

corrected annoying warnings about 'missing initializer'. The memset
version is not better, but gcc like it more.