新增go modules支持，自行管理第三方包依赖，方便开发者使用

third/github.com/golang/snappy/cmd/snappytool/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"io/ioutil"
+	"os"
+
+	"gitee.com/johng/gf/third/github.com/golang/snappy"
+)
+
+var (
+	decode = flag.Bool("d", false, "decode")
+	encode = flag.Bool("e", false, "encode")
+)
+
+func run() error {
+	flag.Parse()
+	if *decode == *encode {
+		return errors.New("exactly one of -d or -e must be given")
+	}
+
+	in, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		return err
+	}
+
+	out := []byte(nil)
+	if *decode {
+		out, err = snappy.Decode(nil, in)
+		if err != nil {
+			return err
+		}
+	} else {
+		out = snappy.Encode(nil, in)
+	}
+	_, err = os.Stdout.Write(out)
+	return err
+}
+
+func main() {
+	if err := run(); err != nil {
+		os.Stderr.WriteString(err.Error() + "\n")
+		os.Exit(1)
+	}
+}