Setting up repo for GitHub pages

This PR includes a one-command approach for publishing to GitHub pages, using [this plugin for Grunt](https://github.com/tschaub/grunt-gh-pages/).

To publish the demo site, just call.

```bash
grunt publish
```

Which will make it available at [http://hitsend.github.io/jQuery-linkify/](http://hitsend.github.io/jQuery-linkify/).