Use Buffer pool to allocate bytes.Buffer for formatter

Entry.Reader() seams not necessary, removed

text_formatter.go

@@ -57,6 +57,7 @@ type TextFormatter struct {
 }
 
 func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
+	var b *bytes.Buffer
 	var keys []string = make([]string, 0, len(entry.Data))
 	for k := range entry.Data {
 		keys = append(keys, k)
@@ -65,8 +66,11 @@ func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
 	if !f.DisableSorting {
 		sort.Strings(keys)
 	}
-
-	b := &bytes.Buffer{}
+	if entry.Buffer != nil {
+		b = entry.Buffer
+	} else {
+		b = &bytes.Buffer{}
+	}
 
 	prefixFieldClashes(entry.Data)