control_callback replaces ping_callback (API Change):

fix #322

The new callback is informed of all frame types including close.

Actions Required:

* Change calls to websocket::stream::ping_callback to use
  websocket::stream::control_callback

* Change user defined ping callbacks to have the new
  signature and adjust the callback definition appropriately.

test/websocket/doc_snippets.cpp

@@ -187,11 +187,11 @@ boost::asio::ip::tcp::socket sock{ios};
 {
     stream<boost::asio::ip::tcp::socket> ws{ios};
 //[ws_snippet_17
-    ws.ping_callback(
-        [](bool is_pong, ping_data const& payload)
+    ws.control_callback(
+        [](frame_type kind, string_view payload)
         {
             // Do something with the payload
-            boost::ignore_unused(is_pong, payload);
+            boost::ignore_unused(kind, payload);
         });
 //]