This changes the interface used to apply a decorator to the HTTP
request or response messages used to perform the WebSocket handshake
as follows:
* Add the `stream_base::decorator` option object
* Add `stream::set_option` overload to set the decorator from
the option
* The decorator applies to all client and server handshakes
performed on the stream after the option is set.
* Overloads of the following functions which accept a Decorator
are deprecated:
- accept, accept_ex
- handshake, handshake_ex
- async_accept, async_accept_ex
- async_handshake, async_handshake_ex
Actions Required:
* Code which passes decorator to any `websocket::stream` member
function should call `stream::set_option` instead with a newly
constructed `stream_base::decorator` object containing the
decorator. Alternatively, the macro `BOOST_BEAST_ALLOW_DEPRECATED`
may be defined to 1.
