Introduce a build process using gulp.js

Hi Lea, thanks for the plugin! I found it very useful so I decided to write a build process for you, replacing the CodeKit workflow that you use at the moment. This will make it easier for collaborators to rebuild minified files as they work on the development javascript.

The build process uses [gulp.js](http://gulpjs.com), the streaming build system. It requires that you have Node (and npm) installed so that you can run it and install the dependencies. To get up and running, once you have Node installed you'll need to run this command in the project root:

```
npm install && npm install -g gulp
```

This will fetch all of the dependencies and install gulp globally to make it easier to run the tasks. Then, to start gulp watching the files for changes, do:

```
gulp watch
```

This will compile `prism.js` and any minified files forever until you stop the watcher with CTRL + C. You can also run compile tasks for each folder without watching, using `gulp build`, `gulp components` and `gulp plugins`.

Note: The minifier seems slightly different to the one that CodeKit is using, some optimisations are different, hence why all of the minified versions have been changed.

I hope this helps! If you have any questions I'll be happy to answer them. :-)
Would make sense to update these dependencies now before merging.