Make shutdown operation thread safe.
Decouple object and container (for example, st_server_socket and st_server).
Drop ssize_t definition for Visual C++.
Version number keeps unchanged.

Add on_close() event, For more change logs, please refer to st_asio_wrapper.h

Split ext/st_asio_wrapper_net.h into ext/st_asio_wrapper_client.h, ext/st_asio_wrapper_server.h and ext/st_asio_wrapper_udp.h.
Add virtual function st_server_base::on_accept_error, it controls whether to continue the acception or not when error occurred.

 st_socket will call on_msg again and again (asynchronously) for the same msg until receive buffer becomes available.

Added a new replaceable buffer shared_buffer.

Fix bug: the last msg will not be re-dispatched if on_msg_handle returned false until new msgs come in.
Drop timer TIMER_SUSPEND_DISPATCH_MSG, it's useless.
Send more msgs in one async_write call.
Fix annotations.

Fix bug: the last msg will not be re-dispatched if on_msg_handle returned false until new msgs come in.
Drop timer TIMER_SUSPEND_DISPATCH_MSG, it's useless.

Fix bug: the last msg will not be re-dispatched if on_msg_handle returned false until new msgs come in.
Drop timer TIMER_SUSPEND_DISPATCH_MSG, it's useless.

Move packers and unpackers out of 'include' directory (now in 'ext' directory), they don't belong to st_asio_wrapper library.
Add pingpong test.
Add streaming unpacker to receive native data.
Support non-copyable msgs.
Make asio_server and test_client more appropriate for performance tunning.