feat(interfaces): adds hashi interfaces

contracts/interfaces/hashi/IAdapter.sol

@@ -0,0 +1,5 @@
+pragma solidity 0.4.24;
+
+interface IAdapter {
+    function getHash(uint256 domain, uint256 id) external view returns (bytes32 hash);
+}

contracts/interfaces/hashi/IReporter.sol

@@ -0,0 +1,15 @@
+pragma solidity 0.4.24;
+
+import "./IAdapter.sol";
+
+interface IReporter {
+    function dispatchBlocks(uint256 targetChainId, IAdapter adapter, uint256[] blockNumbers)
+        external
+        payable
+        returns (bytes32);
+
+    function dispatchMessages(uint256 targetChainId, IAdapter adapter, uint256[] messageIds, bytes32[] messageHashes)
+        external
+        payable
+        returns (bytes32);
+}

contracts/interfaces/hashi/IYaho.sol

@@ -0,0 +1,15 @@
+pragma solidity 0.4.24;
+
+import "./IAdapter.sol";
+import "./IReporter.sol";
+
+interface IYaho {
+    function dispatchMessage(
+        uint256 targetChainId,
+        uint256 threshold,
+        address receiver,
+        bytes data,
+        IReporter[] reporters,
+        IAdapter[] adapters
+    ) external returns (uint256);
+}