fix#767
The write family of HTTP stream algorithms no longer returns
error::end_of_stream when the message indicates that the connection
should be closed.
Actions Required:
* Add code to servers to close the connection after successfully
writing a message where `message::keep_alive()` would return `false`.
* 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.
Vinnie Falco
Peter Jankuliak