Release v2.1.0 solc 0.5.x (#1568)

* Now compiling in a separate directory using truffle 5.

* Ported to 0.5.1, now compiling using 0.5.1.

* test now also compiles using the truffle 5 hack.

* Downgraded to 0.5.0.

* Sorted scripts.

* Cleaned up the compile script a bit.

contracts/mocks/ReentrancyAttack.sol

@@ -1,10 +1,11 @@
-pragma solidity ^0.4.24;
+pragma solidity ^0.5.0;
 
 contract ReentrancyAttack {
 
     function callSender(bytes4 data) public {
         // solium-disable-next-line security/no-low-level-calls
-        require(msg.sender.call(abi.encodeWithSelector(data)));
+        (bool success,) = msg.sender.call(abi.encodeWithSelector(data));
+        require(success);
     }
 
 }