Changes for version 0.12
- Added method "waitfor" as a shortcut for using "job" and "result".
- Moved checks for originating thread to new internal method _check_originating_thread.
- Added method "abort" to have all the worker threads stop after they're finished with their current job. Adapted new, _random and _stream for this new feature.
- Thread::Pool - group of threads for performing similar jobs