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`.
fix#778
* The version data member is replaced with accessor
member functions.
Actions Required:
* Call member function message::version instead of accessing
the version member at call sites.
Vinnie Falco