Apply changed from #9471 Synchronization documentation nits and prepare changes notes for Boost 1.56

	modified:   changes.qbk
	modified:   external_locking.qbk
	modified:   internal_locking.qbk
	modified:   thread.qbk
Update sync queues closed operations
Fix #9335 Missing exception safety might result in crash
Reorganized executors on its own directory adding serial_executor and renamed thread_pool by basic_thread_pool and user_scheduler by loop_scheduler.
fix typo on try_push_back.
executor_adaptor<serial_executor> a(b) doesn't compiles on C++03.
Added missing iomanip include.
Make work public.
Make work public.
Added inline and thread executors.
Added minimal inline and thread test.
Added at thread entry callback on thread pool.
thread changes for WinRT support