Improve comments.

Added documentation about SteamNetConnectionStatusChangedCallback_t.  This is an
important callback, so it's been pretty bad that it was essentially undocumented
until now.

Also use ESteamNetworkingConnectionState instead of int.  (I have taken steps
to make sure that the enum is the right size.)

The notes about ISteamNetworkingUtils::InitializeRelayNetworkAccess are not
 relevant in the opensource context.

Author: zpostfacto

include/steam/isteamnetworkingsockets.h

@@ -83,6 +83,9 @@ class ISteamNetworkingSockets
 	/// in that case, use zero.  If you need to open multiple listen sockets and have clients
 	/// be able to connect to one or the other, then nVirtualPort should be a small integer (<1000)
 	/// unique to each listen socket you create.
+	///
+	/// If you use this, you probably want to call ISteamNetworkingUtils::InitializeRelayNetworkAccess()
+	/// when your app initializes
 	virtual HSteamListenSocket CreateListenSocketP2P( int nVirtualPort ) = 0;
 
 	/// Begin connecting to a server that is identified using a platform-specific identifier.
@@ -93,6 +96,9 @@ class ISteamNetworkingSockets
 	/// Set the SteamID (whether "user" or "gameserver") and Steam will determine if the
 	/// client is online and facilitate a relay connection.  Note that all P2P connections on
 	/// Steam are currently relayed.
+	///
+	/// If you use this, you probably want to call ISteamNetworkingUtils::InitializeRelayNetworkAccess()
+	/// when your app initializes
 	virtual HSteamNetConnection ConnectP2P( const SteamNetworkingIdentity &identityRemote, int nVirtualPort ) = 0;
 #endif
 
@@ -352,12 +358,54 @@ extern "C" {
 #else
 #error "Must define VALVE_CALLBACK_PACK_SMALL or VALVE_CALLBACK_PACK_LARGE"
 #endif
+
+/// This callback is posted whenever a connection is created, destroyed, or changes state.
+/// The m_info field will contain a complete description of the connection at the time the
+/// change occurred and the callback was posted.  In particular, m_eState will have the
+/// new connection state.
+///
+/// You will usually need to listen for this callback to know when:
+/// - A new connection arrives on a listen socket.
+///   m_info.m_hListenSocket will be set, m_eOldState = k_ESteamNetworkingConnectionState_None,
+///   and m_info.m_eState = k_ESteamNetworkingConnectionState_Connecting.
+///   See ISteamNetworkigSockets::AcceptConnection.
+/// - A connection you initiated has been accepted by the remote host.
+///   m_eOldState = k_ESteamNetworkingConnectionState_Connecting, and
+///   m_info.m_eState = k_ESteamNetworkingConnectionState_Connected.
+///   Some connections might transition to k_ESteamNetworkingConnectionState_FindingRoute first.
+/// - A connection has been actively rejected or closed by the remote host.
+///   m_eOldState = k_ESteamNetworkingConnectionState_Connecting or k_ESteamNetworkingConnectionState_Connected,
+///   and m_info.m_eState = k_ESteamNetworkingConnectionState_ClosedByPeer.  m_info.m_eEndReason
+///   and m_info.m_szEndDebug will have for more details.
+///   NOTE: upon receiving this callback, you must still destroy the connection using
+///   ISteamNetworkingSockets::CloseConnection to free up local resources.  (The details
+///   passed to the function are not used in this case, since the connection is already closed.)
+/// - A problem was detected with the connection, and it has been closed by the local host.
+///   The most common failure is timeout, but other configuration or authentication failures
+///   can cause this.  m_eOldState = k_ESteamNetworkingConnectionState_Connecting or
+///   k_ESteamNetworkingConnectionState_Connected, and m_info.m_eState = k_ESteamNetworkingConnectionState_ProblemDetectedLocally.
+///   m_info.m_eEndReason and m_info.m_szEndDebug will have for more details.
+///   NOTE: upon receiving this callback, you must still destroy the connection using
+///   ISteamNetworkingSockets::CloseConnection to free up local resources.  (The details
+///   passed to the function are not used in this case, since the connection is already closed.)
+///
+/// Remember that callbacks are posted to a queue, and networking connections can
+/// change at any time.  It is possible that the connection has already changed
+/// state by the time you process this callback.
+///
+/// Also note that callbacks will be posted when connections are created and destroyed by your own API calls.
 struct SteamNetConnectionStatusChangedCallback_t
 { 
 	enum { k_iCallback = k_iSteamNetworkingSocketsCallbacks + 1 };
-	HSteamNetConnection m_hConn;		//< Connection handle
-	SteamNetConnectionInfo_t m_info;	//< Full connection info
-	int m_eOldState;					//< ESNetSocketState.  (Current stats is in m_info)
+
+	/// Connection handle
+	HSteamNetConnection m_hConn;
+
+	/// Full connection info
+	SteamNetConnectionInfo_t m_info;
+
+	/// Previous state.  (Current state is in m_info.m_eState)
+	ESteamNetworkingConnectionState m_eOldState;
 };
 #pragma pack( pop )