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/mandelbrot_tasks/mandelbrot.cpp

@@ -110,9 +110,6 @@ int main() {
 
     ensureTargetISAIsSupported();
 
-    extern void TasksInit();
-    TasksInit();
-
     int maxIterations = 512;
     int *buf = new int[width*height];