A small optimization for message sending (use message replication rather than parsing message).
Drop direct_broadcast_msg, use broadcast_native_msg instead.

Hide some classes and functions.

ascs::socket's packer() and unpacker() return reference instead of copy to keep the same efficiency as before.

Support UNIX domain socket.
Use std::list instead of ascs::list except the container type of the input queue and out queue in ascs::socket.