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/stencil/stencil.cpp

@@ -102,9 +102,6 @@ void InitData(int Nx, int Ny, int Nz, float *A[2], float *vsq) {
 int main() {
     ensureTargetISAIsSupported();
 
-    extern void TasksInit();
-    TasksInit();
-
     int Nx = 256, Ny = 256, Nz = 256;
     int width = 4;
     float *Aserial[2], *Aispc[2];