fix#769
The following classes are removed:
* handler_type
* async_result
* async_completion
* is_dynamic_buffer
* is_const_buffer_sequence
* is_mutable_buffer_sequence
* handler_alloc
Actions Required:
* Use BOOST_ASIO_HANDLER_TYPE instead of handler_type
* Use BOOST_ASIO_INITFN_RESULT_TYPE instead of async_result
* Use boost::asio::async_completion
* Use boost::asio::is_dynamic_buffer
* Use boost::asio::is_const_buffer_sequence
* Use boost::asio::is_mutable_buffer_sequence
* boost::asio::associated_allocator_t replaces handler_alloc
fix#773
* buffer_prefix is renamed to buffers_prefix
* buffer_prefix_view is renamed to buffers_prefix_view
Actions Required:
* Use buffers_prefix instead of buffer_prefix
* Use buffers_prefix_view instead of buffer_prefix_view
* HTTP read and write operations now return the
number of bytes transferred to or from the stream.
Actions Required:
* Modify HTTP read and/or write completion handlers to receive
the extra std::size_t bytes_transferred parameter.
* stream overloads of accept which take both a message
and a buffer sequence are removed.
Actions Required:
* Do not call websocket accept overloads which take
both a message and a buffer sequence, as it is
illegal per rfc6455.
