Add customizable Logger interface + info,error and debugs (#14)

* Add customizable Logger interface + info,error and debugs
* update travis.yml to atest golang versions

examples/custom-logger/main.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"strconv"
+
+	"gopkg.in/go-playground/webhooks.v3"
+	"gopkg.in/go-playground/webhooks.v3/github"
+)
+
+const (
+	path = "/webhooks"
+	port = 3016
+)
+
+type myLogger struct {
+	PrintDebugs bool
+}
+
+func (l *myLogger) Info(msg string) {
+	log.Println(msg)
+}
+
+func (l *myLogger) Error(msg string) {
+	log.Println(msg)
+}
+
+func (l *myLogger) Debug(msg string) {
+	if !l.PrintDebugs {
+		return
+	}
+	log.Println(msg)
+}
+
+func main() {
+	// webhooks.DefaultLog=webhooks.NewLogger(true)
+	//
+	// or override with your own
+	webhooks.DefaultLog = &myLogger{PrintDebugs: true}
+
+	hook := github.New(&github.Config{Secret: "MyGitHubSuperSecretSecrect...?"})
+	hook.RegisterEvents(HandleMultiple, github.ReleaseEvent, github.PullRequestEvent) // Add as many as you want
+
+	err := webhooks.Run(hook, ":"+strconv.Itoa(port), path)
+	if err != nil {
+		fmt.Println(err)
+	}
+}
+
+// HandleMultiple handles multiple GitHub events
+func HandleMultiple(payload interface{}, header webhooks.Header) {
+	fmt.Println("Handling Payload..")
+
+	switch payload.(type) {
+
+	case github.ReleasePayload:
+		release := payload.(github.ReleasePayload)
+		// Do whatever you want from here...
+		fmt.Printf("%+v", release)
+
+	case github.PullRequestPayload:
+		pullRequest := payload.(github.PullRequestPayload)
+		// Do whatever you want from here...
+		fmt.Printf("%+v", pullRequest)
+	}
+}