Start an asynchronous accept.

template<
    typename Protocol1,
    typename SocketService,
    typename AcceptHandler>
void-or-deduced async_accept(
    implementation_type & impl,
    basic_socket< Protocol1, SocketService > & peer,
    endpoint_type * peer_endpoint,
    AcceptHandler && handler,
    typename enable_if< is_convertible< Protocol, Protocol1 >::value >::type *  = 0);