Improve control message handling documentation

Closes #299

doc.go

@@ -86,20 +86,26 @@
 // and pong. Call the connection WriteControl, WriteMessage or NextWriter
 // methods to send a control message to the peer.
 //
-// Connections handle received close messages by sending a close message to the
-// peer and returning a *CloseError from the the NextReader, ReadMessage or the
-// message Read method.
+// Connections handle received close messages by calling the handler function
+// set with the SetCloseHandler method and by returning a *CloseError from the
+// NextReader, ReadMessage or the message Read method. The default close
+// handler sends a close message to the peer.
 //
-// Connections handle received ping and pong messages by invoking callback
-// functions set with SetPingHandler and SetPongHandler methods. The callback
-// functions are called from the NextReader, ReadMessage and the message Read
-// methods.
+// Connections handle received ping messages by calling the handler function
+// set with the SetPingHandler method. The default ping handler sends a pong
+// message to the peer.
 //
-// The default ping handler sends a pong to the peer. The application's reading
-// goroutine can block for a short time while the handler writes the pong data
-// to the connection.
+// Connections handle received pong messages by calling the handler function
+// set with the SetPongHandler method. The default pong handler does nothing.
+// If an application sends ping messages, then the application should set a
+// pong handler to receive the corresponding pong.
 //
-// The application must read the connection to process ping, pong and close
+// The control message handler functions are called from the NextReader,
+// ReadMessage and message reader Read methods. The default close and ping
+// handlers can block these methods for a short time when the handler writes to
+// the connection.
+//
+// The application must read the connection to process close, ping and pong
 // messages sent from the peer. If the application is not otherwise interested
 // in messages from the peer, then the application should start a goroutine to
 // read and discard messages from the peer. A simple example is: