support for vm.toString() #565
Description
motivation:
the bound cheatcode for signed integers uses vm.toString() when printing the result value. e.g., this test failed due to that.
spec:
/// Converts the given value to a `string`.
function toString(address value) external pure returns (string memory stringifiedValue);
/// Converts the given value to a `string`.
function toString(bytes calldata value) external pure returns (string memory stringifiedValue);
/// Converts the given value to a `string`.
function toString(bytes32 value) external pure returns (string memory stringifiedValue);
/// Converts the given value to a `string`.
function toString(bool value) external pure returns (string memory stringifiedValue);
/// Converts the given value to a `string`.
function toString(uint256 value) external pure returns (string memory stringifiedValue);
/// Converts the given value to a `string`.
function toString(int256 value) external pure returns (string memory stringifiedValue);
the semantics of toString(bytes) isn't clear, but the others should be straightforward.