Use Jekyll, don't keep redundant HTML files

Could you please check if the new pages work for you? A quick visual check has shown no difference for me on Chromium.

- Check out this branch
- In the `website` folder, say `jekyll serve`
- Hit `http://localhost:4000/`

Before merging the pull request and updating the `gh-pages` branch we probably should change the URL from `localhost:4000` to, perhaps, `projecttemplate.net`...