Add rand-seed tool (#710)

tools/rand-seed/main.go

+package main
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+
+	"github.com/mr-tron/base58"
+)
+
+func main() {
+	b := make([]byte, 32)
+	_, err := rand.Read(b)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	fmt.Printf("base64:%s\n", base64.StdEncoding.EncodeToString(b))
+	fmt.Printf("base58:%s\n", base58.Encode(b))
+}