add hardhat, compile MIPS contract

.gitignore

 node_modules
+artifacts
+cache

contracts/MIPS.sol

-pragma solidity ^0.8.0;
+pragma solidity ^0.7.3;
 // https://inst.eecs.berkeley.edu/~cs61c/resources/MIPS_Green_Sheet.pdf
 // https://uweb.engr.arizona.edu/~ece369/Resources/spim/MIPSReference.pdf
 

hardhat.config.js

+/**
+ * @type import('hardhat/config').HardhatUserConfig
+ */
+module.exports = {
+  solidity: "0.7.3",
+};

package.json

@@ -2,6 +2,7 @@
   "dependencies": {
     "@types/node": "^16.9.2",
     "ethers": "^5.4.7",
+    "hardhat": "^2.6.4",
     "rlp": "^2.2.6",
     "typescript": "^4.4.3"
   }