Experimenting with multiple sol versions (#30)

packages/contracts/contracts/optimistic-ethereum/iOVM/accounts/iOVM_ECDSAContractAccount.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/bridge/iOVM_BaseCrossDomainMessenger.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /**
@@ -19,7 +19,7 @@ interface iOVM_BaseCrossDomainMessenger {
      */
     function sendMessage(
         address _target,
-        bytes memory _message,
+        bytes calldata _message,
         uint256 _gasLimit
     ) external;
 }

packages/contracts/contracts/optimistic-ethereum/iOVM/bridge/iOVM_L1CrossDomainMessenger.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/bridge/iOVM_L2CrossDomainMessenger.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Interface Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/chain/iOVM_CanonicalTransactionChain.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/chain/iOVM_StateCommitmentChain.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/execution/iOVM_ExecutionManager.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/execution/iOVM_SafetyChecker.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /**
  * @title iOVM_SafetyChecker
@@ -10,5 +10,5 @@ interface iOVM_SafetyChecker {
      * Public Functions *
      ********************/
 
-    function isBytecodeSafe(bytes memory _bytecode) external view returns (bool);
+    function isBytecodeSafe(bytes calldata _bytecode) external view returns (bool);
 }

packages/contracts/contracts/optimistic-ethereum/iOVM/execution/iOVM_StateManager.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/execution/iOVM_StateManagerFactory.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /* Contract Imports */
 import { iOVM_StateManager } from "./iOVM_StateManager.sol";

packages/contracts/contracts/optimistic-ethereum/iOVM/precompiles/iOVM_DeployerWhitelist.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /**
  * @title iOVM_DeployerWhitelist

packages/contracts/contracts/optimistic-ethereum/iOVM/precompiles/iOVM_L1MessageSender.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /**
  * @title iOVM_L1MessageSender

packages/contracts/contracts/optimistic-ethereum/iOVM/precompiles/iOVM_L2ToL1MessagePasser.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /**
  * @title iOVM_L2ToL1MessagePasser
@@ -21,5 +21,5 @@ interface iOVM_L2ToL1MessagePasser {
      * Public Functions *
      ********************/
     
-    function passMessageToL1(bytes memory _message) external;
+    function passMessageToL1(bytes calldata _message) external;
 }

packages/contracts/contracts/optimistic-ethereum/iOVM/verification/iOVM_BondManager.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 interface ERC20 {
     function transfer(address, uint256) external returns (bool);

packages/contracts/contracts/optimistic-ethereum/iOVM/verification/iOVM_FraudVerifier.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/verification/iOVM_StateTransitioner.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 pragma experimental ABIEncoderV2;
 
 /* Library Imports */

packages/contracts/contracts/optimistic-ethereum/iOVM/verification/iOVM_StateTransitionerFactory.sol

 // SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.7.0;
+pragma solidity >0.5.0 <0.8.0;
 
 /* Contract Imports */
 import { iOVM_StateTransitioner } from "./iOVM_StateTransitioner.sol";