Clean up WRT prefix.
Rename.
Fix build.
Use sane header guard.
Misc fixes.

 * Use C99.
   autoconf has builtin C99 checker, so use it.
 * Use malloc() if sbrk() not found.
 * Add more AC_CHECK_FUNCS.
 * Use defined() macros.
 * Use bdw-gc style export function name.
   Also, fix invalid header guard which was inverted accidentaly.
 * Include config.h.
 * Use binary presentation for flag definition.
 * Remove useless #ifdef business for TINY_HEAP_SIZE.
   The default should be set on configure, or enabled to tune on init
   is the way to go.
   Also, this chageset author, sora_h is removed from AUTHORS.
 * Slay Camels, be snake.
 * Remove pointless prefix gc.
   Also do not use mingc prefix for internal functions.
 * Remove unused variables.
 * Remove pointless size_t signed check.
   This is clearly unsined.
 * Use bool for boolean flag, not size_t.
 * No more declare simple local variables at beginning of function.