Add example for using timer to measure its own performance

examples/timer-performance.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"github.com/azer/logger"
+)
+
+func main() {
+
+	var perf = logger.New("performance")
+	var test = logger.New("test")
+
+	timer := perf.Timer()
+	for i := 0; i < 999999; i++ {
+		t := test.Timer()
+		t.End("foobar", logger.Attrs{
+			"foo": 123,
+			"bar": true,
+		})
+	}
+	timer.End("End")
+}