[Tech Debt]: started the CLI work for PR#49

This pull requests includes the very basic work to start end-to-end testing the arithmetic CLI integration

https://github.com/jspm/jspm-cli/issues/49
I think the code can just be - 

```javascript
cast 'bundle':
  // check if second last argument is a sign
  var secondLastArg = args[args.length - 2].trim();
  var signChar = secondLastArg.substr(secondLastArg.length - 1, 1);
  if (signChar == '+' || signChar == '-' || signChar == '*') {
    core.bundle(args.join(' '), 'bundle.js');
  }
  else {
    core.bundle(args.splice(0, args.length - 1).join(' '), args[args.length - 1]);
  }
}
```