[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
The only parsing necessary here is exactly the code example above, with an `isSign` function (basically just checking equality with `-`, `+`, or `*`).

I do think this is important as otherwise we break backwards compatibility.