Adds tool to issue data msgs on a remote node (#560)

* adds tool to issue data msgs on a remote node

* gofmt yourself

tools/spammer/main.go

+package main
+
+import (
+	"fmt"
+
+	"github.com/iotaledger/goshimmer/client"
+	flag "github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+const (
+	cfgNodeURI = "node"
+	cfgMessage = "message"
+)
+
+func init() {
+	flag.String(cfgNodeURI, "http://127.0.0.1:8080", "the URI of the node API")
+	flag.String(cfgMessage, "", "the URI of the node API")
+}
+
+func main() {
+	flag.Parse()
+	if err := viper.BindPFlags(flag.CommandLine); err != nil {
+		panic(err)
+	}
+	goshimAPI := client.NewGoShimmerAPI(viper.GetString(cfgNodeURI))
+	messageBytes := []byte(viper.GetString(cfgMessage))
+	var issued, failed int
+	for {
+		fmt.Printf("issued %d, failed %d\r", issued, failed)
+		_, err := goshimAPI.Data(messageBytes)
+		if err != nil {
+			failed++
+			continue
+		}
+		issued++
+	}
+}