fix get on json

添加get模式支持json 标签，主要用于proto自动生成文件

internal/bytesconv/bytesconv.go

@@ -0,0 +1,24 @@
+// Copyright 2020 Gin Core Team. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package bytesconv
+
+import (
+	"unsafe"
+)
+
+// StringToBytes converts string to byte slice without a memory allocation.
+func StringToBytes(s string) []byte {
+	return *(*[]byte)(unsafe.Pointer(
+		&struct {
+			string
+			Cap int
+		}{s, len(s)},
+	))
+}
+
+// BytesToString converts byte slice to string without a memory allocation.
+func BytesToString(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}