moving to Intel Threading Blocks

deeper and deeper into concurrency and multi threading...

I have decision to use Intel Threading Building Blocks instead of experimental boost::thread_pool. All computations in the Glow engine are organized into tasks and theoretically would scale well when number of hardware threads (CPU cores) will be increased.

Previously, I used boost::thread_pool for task execution. Now, when I returned to concurrency, I realized that usage of boost::thread_pool is not scalable, because it heavily uses mutexes (spin-based). Later I will launch tests to measure scalability of both methods and post results here.