Tweak fargoPublisher for Heroku deployment

Just a few minor tweaks and some docs to get you started.  Here's what
I changed:

1. I added a `.gitignore` file to hide the `node_modules` directory from
   git.  This isn't necessary, but it makes it possible to test
   `npm install` on the local system without generating lots of noisy
   git output.
2. `Procfile` contains a single line describing how to run the web server.
3. `package.json` has a three-part version number, which makes `npm
   install` happier.  We need this so Heroku can run `npm install` to
   install all the Node packages on the server for us.
4. `publisher.js` now gets its port from `PORT`, which is where Heroku
   puts it.