Remove websocket::keep_alive option (API Change):

fix #332

This removes the keep_alive option from the WebSocket stream.
Callers who wish to control the behavior of the Connection
header may do so in the decorator and completion handlers
for the handshake and accept functions.

test/websocket/stream.cpp

@@ -541,7 +541,6 @@ public:
     {
         stream<socket_type> ws(ios_);
         ws.set_option(auto_fragment{true});
-        ws.set_option(keep_alive{false});
         ws.set_option(write_buffer_size{2048});
         ws.set_option(message_type{opcode::text});
         ws.set_option(read_buffer_size{8192});
@@ -992,7 +991,6 @@ public:
                 {
                     stream<test::string_istream> ws(ios_,
                         s.substr(i, s.size() - i));
-                    ws.set_option(keep_alive{true});
                     try
                     {
                         ws.accept(boost::asio::buffer(