Make it easier for an exercism user to run tests for an assignment

[rchavarria]

I struggled a little bit while running my code for the palindrome-products assignment, so I was wondering if there could be a better way to run them.

I was thinking of having a package.json file (as if the assignment was a NodeJS module) and a gulpfile.js file, to have all the work automated in a Gulp script.

But I'm not sure if this is compatible with exercism's philosophy. The exercism user must have installed NodeJS (I think this is acceptable) and she must first install gulp-cli tool so that she can run then the Gulp script. Then, for each assignment, the idea is that the user has just to run a npm install command at the beginning, and npm test or gulp test every time she wants to run her tests.

If this way of working on ecmascript assignments is ok, I'll implement it on the existing one, palindrome-products, and I'll make a pull request.

[kytrinyx]

I think that it would be fine to have gulp, as long as the version with fewer dependencies is documented, and gulp is a "nice to have". Anything to make it easier to get started is a good thing, I think.

[rchavarria]

Fixed with the old Pull Request #13