feat: expand non-evm relay and route planning support

contracts/vendor/uniswap-v2-core/libraries/SafeMath.sol

@@ -0,0 +1,17 @@
+pragma solidity =0.5.16;
+
+// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)
+
+library SafeMath {
+    function add(uint x, uint y) internal pure returns (uint z) {
+        require((z = x + y) >= x, 'ds-math-add-overflow');
+    }
+
+    function sub(uint x, uint y) internal pure returns (uint z) {
+        require((z = x - y) <= x, 'ds-math-sub-underflow');
+    }
+
+    function mul(uint x, uint y) internal pure returns (uint z) {
+        require(y == 0 || (z = x * y) / y == x, 'ds-math-mul-overflow');
+    }
+}