Add StatusCode library

contracts/libraries/StatusCodes.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.5.0;
+
+library StatusCodes {
+
+    // ERC1400 status code inspired from ERC1066
+    enum Status { 
+        TransferFailure,
+        TransferSuccess,
+        InsufficientBalance,
+        InsufficientAllowance,
+        TransfersHalted,
+        FundsLocked,
+        InvalidSender,
+        InvalidReceiver,
+        InvalidOperator
+    }
+
+    function code(Status _status) internal pure returns (byte) {
+        return byte(uint8(0x50) + (uint8(_status)));
+    }
+}

contracts/libraries/TokenLib.sol

@@ -1,6 +1,7 @@
 pragma solidity ^0.5.0;
 
 import "../interfaces/IPoly.sol";
+import "./StatusCodes.sol";
 import "../modules/UpgradableModuleFactory.sol";
 import "../interfaces/IDataStore.sol";
 import "../tokens/SecurityTokenStorage.sol";
@@ -450,9 +451,9 @@ library TokenLib {
             // If no unarchived modules, return true by default
             // Use the local variables to avoid the stack too deep error
             isValid = transfersFrozen ? (isForceValid ? true : (isInvalid ? false : isValid)) : true;
-            return (isValid, isValid ? bytes32(hex"51"): appCode);
+            return (isValid, isValid ? bytes32(StatusCodes.code(StatusCodes.Status.TransferSuccess)): appCode);
         }
-        return (false, bytes32(hex"54"));
+        return (false, bytes32(StatusCodes.code(StatusCodes.Status.TransfersHalted)));
     }
 
     function canTransfer(
@@ -467,19 +468,19 @@ library TokenLib {
         returns (bool, byte, bytes32)
     {
         if (!success)
-            return (false, 0x50, appCode);
+            return (false, StatusCodes.code(StatusCodes.Status.TransferFailure), appCode);
 
         if (balanceOfFrom < value)
-            return (false, 0x52, bytes32(0));
+            return (false, StatusCodes.code(StatusCodes.Status.InsufficientBalance), bytes32(0));
 
         if (to == address(0))
-            return (false, 0x57, bytes32(0));
+            return (false, StatusCodes.code(StatusCodes.Status.InvalidReceiver), bytes32(0));
 
         // Balance overflow can never happen due to totalsupply being a uint256 as well
         // else if (!KindMath.checkAdd(balanceOf(_to), _value))
         //     return (false, 0x50, bytes32(0));
 
-        return (true, 0x51, bytes32(0));
+        return (true, StatusCodes.code(StatusCodes.Status.TransferSuccess), bytes32(0));
     }
 
     function _getKey(bytes32 _key1, address _key2) internal pure returns(bytes32) {

contracts/tokens/SecurityToken.sol

@@ -5,6 +5,7 @@ import "../PolymathRegistry.sol";
 import "../interfaces/IModule.sol";
 import "./SecurityTokenStorage.sol";
 import "../libraries/TokenLib.sol";
+import "../libraries/StatusCodes.sol";
 import "../interfaces/IDataStore.sol";
 import "../interfaces/IUpgradableTokenFactory.sol";
 import "../interfaces/IModuleFactory.sol";
@@ -934,15 +935,15 @@ contract SecurityToken is ERC20, ReentrancyGuard, SecurityTokenStorage, IERC1594
     function canTransferFrom(address _from, address _to, uint256 _value, bytes calldata _data) external view returns (bool success, byte reasonCode, bytes32 appCode) {
         (success, reasonCode, appCode) = _canTransfer(_from, _to, _value, _data);
         if (success && _value > allowance(_from, msg.sender)) {
-            return (false, 0x53, bytes32(0));
+            return (false, StatusCodes.code(StatusCodes.Status.InsufficientAllowance), bytes32(0));
         }
     }
 
     function _canTransfer(address _from, address _to, uint256 _value, bytes memory _data) internal view returns (bool, byte, bytes32) {
         bytes32 appCode;
         bool success;
         if (_value % granularity != 0) {
-            return (false, 0x50, bytes32(0));
+            return (false, StatusCodes.code(StatusCodes.Status.TransferFailure), bytes32(0));
         }
         (success, appCode) = TokenLib.verifyTransfer(modules[TRANSFER_KEY], modulesToData, _from, _to, _value, _data, transfersFrozen);
         return TokenLib.canTransfer(success, appCode, _to, _value, balanceOf(_from));
@@ -981,7 +982,7 @@ contract SecurityToken is ERC20, ReentrancyGuard, SecurityTokenStorage, IERC1594
             }
             return (esc, appStatusCode, toPartition);
         }
-        return (0x50, bytes32(0), bytes32(0));
+        return (StatusCodes.code(StatusCodes.Status.TransferFailure), bytes32(0), bytes32(0));
     }
 
     /**