restruct contract repo

contracts/intf/IFeeRateModel.sol

@@ -0,0 +1,14 @@
+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+pragma experimental ABIEncoderV2;
+
+
+interface IFeeRateModel {
+    function getFeeRate(uint256 amount) external view returns (uint256);
+}