Add support for pointer values in Fields

Fixes #46

fields.go

@@ -54,6 +54,38 @@ func appendFields(dst []byte, fields map[string]interface{}) []byte {
 			dst = json.AppendTime(dst, val, TimeFieldFormat)
 		case time.Duration:
 			dst = json.AppendDuration(dst, val, DurationFieldUnit, DurationFieldInteger)
+		case *string:
+			dst = json.AppendString(dst, *val)
+		case *bool:
+			dst = json.AppendBool(dst, *val)
+		case *int:
+			dst = json.AppendInt(dst, *val)
+		case *int8:
+			dst = json.AppendInt8(dst, *val)
+		case *int16:
+			dst = json.AppendInt16(dst, *val)
+		case *int32:
+			dst = json.AppendInt32(dst, *val)
+		case *int64:
+			dst = json.AppendInt64(dst, *val)
+		case *uint:
+			dst = json.AppendUint(dst, *val)
+		case *uint8:
+			dst = json.AppendUint8(dst, *val)
+		case *uint16:
+			dst = json.AppendUint16(dst, *val)
+		case *uint32:
+			dst = json.AppendUint32(dst, *val)
+		case *uint64:
+			dst = json.AppendUint64(dst, *val)
+		case *float32:
+			dst = json.AppendFloat32(dst, *val)
+		case *float64:
+			dst = json.AppendFloat64(dst, *val)
+		case *time.Time:
+			dst = json.AppendTime(dst, *val, TimeFieldFormat)
+		case *time.Duration:
+			dst = json.AppendDuration(dst, *val, DurationFieldUnit, DurationFieldInteger)
 		case []string:
 			dst = json.AppendStrings(dst, val)
 		case []bool:

log_test.go

@@ -135,6 +135,32 @@ func TestFieldsMap(t *testing.T) {
 	}
 }
 
+func TestFieldsMapPnt(t *testing.T) {
+	out := &bytes.Buffer{}
+	log := New(out)
+	log.Log().Fields(map[string]interface{}{
+		"string":  new(string),
+		"bool":    new(bool),
+		"int":     new(int),
+		"int8":    new(int8),
+		"int16":   new(int16),
+		"int32":   new(int32),
+		"int64":   new(int64),
+		"uint":    new(uint),
+		"uint8":   new(uint8),
+		"uint16":  new(uint16),
+		"uint32":  new(uint32),
+		"uint64":  new(uint64),
+		"float32": new(float32),
+		"float64": new(float64),
+		"dur":     new(time.Duration),
+		"time":    new(time.Time),
+	}).Msg("")
+	if got, want := out.String(), `{"bool":false,"dur":0,"float32":0,"float64":0,"int":0,"int16":0,"int32":0,"int64":0,"int8":0,"string":"","time":"0001-01-01T00:00:00Z","uint":0,"uint16":0,"uint32":0,"uint64":0,"uint8":0}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+}
+
 func TestFields(t *testing.T) {
 	out := &bytes.Buffer{}
 	log := New(out)