Adding ability to customize thread priority, thread stack size and targeted processing unit to the default_executor. Added corresponding example.
Adding new APIs: hpx::this_thread::get_stack_size() and hpx::threads::get_statck_size_name()
Fixing handling of task execution policy embedded in a dynamic execution_policy
Adding more docs for task regions
Merge branch 'master' into parallel_rotate
More fixes for rotate_copy