Allow to skip specifying logger so default log package will be used.

exported.go

@@ -23,12 +23,26 @@
 
 package flagger
 
+import (
+	// stdlib
+	"log"
+	"os"
+)
+
 var (
 	logger LoggerInterface
 )
 
+// New creates new Flagger instance.
+// If no logger will be passed - we will use default "log" module and will
+// print logs to stdout.
 func New(l LoggerInterface) *Flagger {
+	if l == nil {
+		lg := log.New(os.Stdout, "Flagger: ", log.LstdFlags)
+		logger = LoggerInterface(lg)
+	} else {
 		logger = l
+	}
 	f := Flagger{}
 	return &f
 }

flagger_test.go

@@ -43,6 +43,15 @@ func TestFlaggerInitialization(t *testing.T) {
 	f.Initialize()
 }
 
+func TestFlaggerInitializationWithNilLogger(t *testing.T) {
+	fl := New(nil)
+	if f == nil {
+		t.Fatal("Logger initialization failed!")
+		t.FailNow()
+	}
+	fl.Initialize()
+}
+
 func TestFlaggerAddBoolFlag(t *testing.T) {
 	flagTestBool := Flag{
 		Name:         "testboolflag",