Various improvements to example task systems in examples/.

- Only have a single copy of all of the tasks_*.cpp sample implementations,
  stored in examples/.
- Reduce dynamic storage allocation and locking in task launch code paths.
- Don't have a hard limit of the number of tasks that can be launched on
  Windows (fix issue #85).

examples/rt/rt.cpp

@@ -134,9 +134,6 @@ int main(int argc, char *argv[]) {
 
     ensureTargetISAIsSupported();
 
-    extern void TasksInit();
-    TasksInit();
-
 #define READ(var, n)                                            \
     if (fread(&(var), sizeof(var), n, f) != (unsigned int)n) {  \
         fprintf(stderr, "Unexpected EOF reading scene file\n"); \