initial code (#6)

* initial code commit

cache/put.go

@@ -0,0 +1,16 @@
+package cache
+
+import (
+	"fmt"
+	"github.com/xujiajun/nutsdb"
+	"time"
+)
+
+func (c *Client) Put(bucket string, key string, val []byte, ttl time.Duration) error {
+	if err := c.db.Update(func(tx *nutsdb.Tx) error {
+		return tx.Put(bucket, []byte(key), val, uint32(ttl.Seconds()))
+	}); err != nil {
+		return fmt.Errorf("%v: %v; put: %w", bucket, key, err)
+	}
+	return nil
+}