add dsp pool

contracts/DODOStablePool/intf/IDSP.sol

@@ -0,0 +1,36 @@
+/*
+
+    Copyright 2020 DODO ZOO.
+    SPDX-License-Identifier: Apache-2.0
+
+*/
+
+pragma solidity 0.6.9;
+pragma experimental ABIEncoderV2;
+
+interface IDSP {
+    function init(
+        address maintainer,
+        address baseTokenAddress,
+        address quoteTokenAddress,
+        uint256 lpFeeRate,
+        address mtFeeRateModel,
+        uint256 i,
+        uint256 k,
+        bool isOpenTWAP
+    ) external;
+
+    function _BASE_TOKEN_() external returns (address);
+
+    function _QUOTE_TOKEN_() external returns (address);
+
+    function _MT_FEE_RATE_MODEL_() external returns (address);
+
+    function getVaultReserve() external returns (uint256 baseReserve, uint256 quoteReserve);
+
+    function sellBase(address to) external returns (uint256);
+
+    function sellQuote(address to) external returns (uint256);
+
+    function buyShares(address to) external returns (uint256);
+}