add level type function

Author: mobus

examples/log/log_ex.go

@@ -1,12 +1,30 @@
 package main
 
-import "github.com/sunvim/utils/log"
+import (
+	"fmt"
+
+	"github.com/sunvim/utils/log"
+)
 
 func main() {
-	log.SetPrefix("Hello")
+	log.SetPrefix("Example")
+
+	fmt.Println("debug level")
+	log.SetLevel(log.LevelDebug)
+	log.Debug("hello debug")
+	log.Info("hello info")
+	log.Error("hello error")
 
-	log.Info("info hello log")
+	fmt.Println("info level")
+	log.SetLevel(log.LevelInfo)
+	log.Debug("hello debug")
+	log.Info("hello info")
+	log.Error("hello error")
 
-	log.Error("error log")
+	fmt.Println("error level")
+	log.SetLevel(log.LevelError)
+	log.Debug("hello debug")
+	log.Info("hello info")
+	log.Error("hello error")
 
 }