feat: adds ERC20 permit interface, ref. eip-2612 (#80)

Author: scnale

src/interfaces/token/IERC20Permit.sol

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: Apache 2
+
+pragma solidity ^0.8.0;
+
+import "IERC20/IERC20.sol";
+
+//https://eips.ethereum.org/EIPS/eip-2612
+interface IERC20Permit is IERC20 {
+  function permit(
+    address owner,
+    address spender,
+    uint value,
+    uint deadline,
+    uint8 v,
+    bytes32 r,
+    bytes32 s
+  ) external;
+  function nonces(address owner) external view returns (uint);
+  function DOMAIN_SEPARATOR() external view returns (bytes32);
+}