Comments and unused consts

This tidies up comments as per issues #254 and #274 and removes unused constants.

autopaho/auto.go

@@ -87,7 +87,7 @@ type ClientConfig struct {
 	// To fix, use packets.NewThreadSafeConn wrapper or extend the custom net.Conn struct with sync.Locker.
 	AttemptConnection func(context.Context, ClientConfig, *url.URL) (net.Conn, error)
 
-	OnConnectionUp func(*ConnectionManager, *paho.Connack) // Called (within a goroutine) when a connection is made (including reconnection). Connection Manager passed to simplify subscriptions.
+	OnConnectionUp func(*ConnectionManager, *paho.Connack) // Called when a connection is made (including reconnection). Connection Manager passed to simplify subscriptions. Supplied function must not block.
 	OnConnectError func(error)                             // Called (within a goroutine) whenever a connection attempt fails. Will wrap autopaho.ConnackError on server deny.
 
 	Debug      log.Logger // By default set to NOOPLogger{},set to a logger for debugging info

paho/client.go

@@ -31,13 +31,6 @@ import (
 	"github.com/eclipse/paho.golang/paho/session/state"
 )
 
-type MQTTVersion byte
-
-const (
-	MQTTv311 MQTTVersion = 4
-	MQTTv5   MQTTVersion = 5
-)
-
 const defaultSendAckInterval = 50 * time.Millisecond
 
 var (
@@ -91,7 +84,8 @@ type (
 		PacketTimeout time.Duration
 		// OnServerDisconnect is called only when a packets.DISCONNECT is received from server
 		OnServerDisconnect func(*Disconnect)
-		// OnClientError is for example called on net.Error
+		// OnClientError is for example called on net.Error. Note that this may be called multiple times and may be
+		// called following a successful `Disconnect`. See autopaho.errorHandler for an example.
 		OnClientError func(error)
 		// PublishHook allows a user provided function to be called before
 		// a Publish packet is sent allowing it to inspect or modify the