[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
In terms of detecting if `build.js` is present the process could be like this:

```javascript
// check if second last argument is a sign
var secondLastArg = args[args.length - 2].trim();
if (isSign(secondLastArg.substr(secondLastArg.length - 1, 1)) {
  // we now know that the build file is not specified
}
```