[UPDATED] Examples moved to their own directory

Each example has been moved to its own directory (and .go file changed
to main.go, and build directive removed).
With this change, once you `go get` the library, you can intall
all examples with the following command:

```
go install github.com/nats-io/go-nats-streaming/examples/*
```

Also fixed some issues reported by megacheck.

Resolves #164

examples/stan-pub.go → examples/stan-pub/main.go

@@ -1,5 +1,4 @@
 // Copyright 2012-2016 Apcera Inc. All rights reserved.
-// +build ignore
 
 package main
 
@@ -79,7 +78,7 @@ func main() {
 		ch <- true
 	}
 
-	if async != true {
+	if !async {
 		err = sc.Publish(subj, msg)
 		if err != nil {
 			log.Fatalf("Error during publish: %v\n", err)

examples/stan-sub.go → examples/stan-sub/main.go

@@ -1,5 +1,4 @@
 // Copyright 2012-2016 Apcera Inc. All rights reserved.
-// +build ignore
 
 package main
 
@@ -106,9 +105,9 @@ func main() {
 
 	if startSeq != 0 {
 		startOpt = stan.StartAtSequence(startSeq)
-	} else if deliverLast == true {
+	} else if deliverLast {
 		startOpt = stan.StartWithLastReceived()
-	} else if deliverAll == true {
+	} else if deliverAll {
 		log.Print("subscribing with DeliverAllAvailable")
 		startOpt = stan.DeliverAllAvailable()
 	} else if startDelta != "" {
@@ -138,7 +137,7 @@ func main() {
 	cleanupDone := make(chan bool)
 	signal.Notify(signalChan, os.Interrupt)
 	go func() {
-		for _ = range signalChan {
+		for range signalChan {
 			fmt.Printf("\nReceived an interrupt, unsubscribing and closing connection...\n\n")
 			// Do not unsubscribe a durable on exit, except if asked to.
 			if durable == "" || unsubscribe {