Fix malformed HTML

The HTML for the example experiment doesn't always quite conform to correct HTML syntax. This pull request just makes a few minor formatting changes, including:

* capitalizing DOCTYPE
* including a `<meta>` tag for the encoding (utf-8)
* closing various tags, like `<link />` and `<hr />` and `<br />`
* putting quotes around `stylesheet` in `<link rel="stylesheet" />`
* inserting a few missing closing tags
* specifying script and style types